Modern Concept Science and Technology 10

146 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 14710. Extinct species : The species whose populations are already zero on the earth are called extinct species.11. Endangered animals : The animals whose populations have significantly dropped and are at risk of extinction are called endangered or rare animals. 12. Endangered plants : The plants whose numbers have significantly dropped and are at risk of extinction are called endangered or rare plants.13. Control of International Trade of Endangered Wild Fauna and Flora Act, 2073 : Nepal government has launched the Control of International Trade of Endangered Wild Fauna and Flora Act, 2073 to prevent poaching and smuggling of endangered plants and animals. 14. In-situ conservation : The process of conservation of organisms in their natural habitat is called in-situ conservation. For example, protecting Bengal tigers in national parks.15. Ex-situ conservation : The process of conservation of organisms outside their natural habitat or in manmade habitat is called ex-situ conservation. For example, protecting tigers in zoos or research labs. 16. Protected plants and animals: The plants, animals and birds that are banned by the law to harm or destroy are called protected species. 17. Protected area : The huge area separated by the government for the conservation of endangered species is called a protected area. Most of the protected animals are in protected areas.18. Medicinal plants : The plants whose various parts are used in traditional medicine are called medicinal plants. 19. Holy basil (tulsi) : Holy basil (Ocimum sanctum) is a small annual or perennial shrub with a fragrant leaf. 20. Neem : Neem (Azadirachta indica) is a tree. It is used to purify blood, cure skin diseases, reduce bad cholesterol and reduce high blood pressure. 21. Heart-leaved moonseed (gurjo) : Heart-leaved moonseed (Tinospora cordifolia) is a climber plant. It reproduces usually by vegetative propagation by stem. 22. Asiatic pennywort (ghodtapre) : Asiatic pennywort (Centella asiatica) is a perennial climber plant. It grows in moist and shady places. It is grown because it has antioxidant and antimicrobial properties. 23. Turmeric (beshar) : Turmeric (Curcuma longa) is a perennial herb rich in curcumin, vitamins A, B, B2, C, phosphorus, iron and calcium. 24. Malabar nuts (ashuro) : Malabar nuts (Adhatoda vasica) is a medicinal herb found in the Chure hills and Mahabharat range of Nepal. It is rich in hydroxy vasicine, vasicinone and vasicine. 25. Calamus (bhojo) : Calamus (Acorus calamus) is a perennial herb that grows in wetlands. It is grown for its rhizome which can treat cough, sore throat and stomach ache. 26. Chinese caterpillar fungus (Yarshagumba) : Yarshagumba (Cordyceps sinensis) is a parasitic fungus that grows on a caterpillar. 27. Mugwort (titepate) : Mugwort (Artemisia vulgaris) is a medicinal shrub that grows in the mid-hills of Nepal. 28. Aloevera (Ghiukumari) : Ghiukumari (Aloe vera) is a xerophyte with fleshy leaves and thorns. It is grown for its gel and juice. It is rich in vitamins A and C.

148 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 149Climate The weather and climate of a place are its atmospheric conditions at a particular time. If we observe a short period, the atmospheric condition keeps changing a lot. We call it weather. The change in the day-to-day condition of the atmosphere is called weather. It could be a sunny day, cold day, rainy day, cloudy day and windy day. The condition of the atmosphere that remains almost the same for a few months is called season. However, the atmospheric condition of a wide region that remains almost the same for at least 30 years is called a climate. Climate is a delicate phenomenon. It can change over time due to multiple factors. Sunshine, the amount of greenhouse gases in the atmosphere, industrialization, deforestation, solar activities, natural disasters and many other things affect the weather and climate of a place. Climate ChangeClimate can change naturally. However, human activities increase the rate of climate change. The process in which the atmospheric condition of a huge area differs gradually over a very long time due to natural activity or human activities is called climate change. The most important gas that plays a crucial role in the state of the climate of a place is carbon dioxide. The fuel obtained by burning fossils such as coal and petroleum is called fossil fuel. Coal, petrol, diesel and LPG gas are fossil fuels. They are major sources of carbon dioxide gas. Carbon dioxide gas is a greenhouse gas. The gases that can trap heat energy and significantly change the temperature of the atmosphere are called greenhouse gases. For example, carbon dioxide, water vapour, methane etc. They are responsible for climate change. The process by which greenhouse gases such as carbon dioxide, water vapour, etc. can trap solar energy and increase the temperature of the earth is called the greenhouse effect. It continuously increases the temperature of the earth. The process in which the over-greenhouse effect increases the temperature of the earth gradually is called global warming. The greenhouse gases from natural sources or human-made infrastructures cause excessive greenhouse effect, which leads to global warming and ultimately changes the climate. Climate change is a fact. Various research, scientific reports, data from weather stations and satellite images account for climate change. Nepal is also heavily affected by climate change. The temperature of Nepal is increasing by 0.06°C each year. The continuous temperature rise has caused climate change in Nepal. Some of the consequences of climate change in Nepal are winters are shorter, irregular rainfall, lesser rainfall in monsoon, the spread of diseases such as dengue even in hilly regions, a decrease in agricultural production because plants cannot grow well, less snowfall than regular, lack of snow in the hills, less water in the river and pond, lack of water for irrigation and drinking, lack of water in the dam of hydropower station, less production of electricity, energy crisis, melting of snow has increased water volume and water pressure in glacier lakes and risk of glacier lake outburst flood (GLOF) has increased. To adapt and mitigate climate change the Nepal government has tried to raise public

148 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 149awareness, declare protected areas, prevent deforestation, launch afforestation programs, promote electricity for fuel, promote electric vehicles and make rules, regulations and policies to reduce climate change. They have launched the Environment Conservation Act. Environment Conservation Act 2076 has directed the central government, local government, private sector and province administration should plan and implement activities to reduce climate change and adapt to climate change. The Nepal government has encouraged people to use electric vehicles. Many electric Sajha buses are also in operation in the effort of the government. Nepal's government has made many protected areas such as wildlife areas, conservation areas and national parks. These areas protect wildlife. The vast area of forest is conserved here, which helps to reduce carbon dioxide from the air and reduce the effect of climate change. Nepal's government has launched many programs to raise awareness among its citizens about climate change and its effects.Causes of Climate changeA. Natural causes of climate changeThe different types of natural phenomenon like volcano, evaporation, emission of green house gases, etc. are responsible for climate change.1. Change in solar activityThe sun is the ultimate source of heat energy for Earth. The thermonuclear fusion reaction at the core of the sun is the source of the tremendous amount of heat and light. If the rate of nuclear reaction changes, the intensity of the sunlight also changes. So, if intense sunlight comes towards Earth or a huge solar flare occurs facing the Earth, a huge amount of solar radiation will enter the Earth. It could change the temperature of the earth and bring climate changes. 2. Change in the reflection of the sun lightIf the ozone layer is depleted excessive amounts of sunlight will enter the earth. The earth’s atmosphere will absorb large amounts of heat. The average temperature of the earth increases and climate will change. Usually, 70% of the solar radiation are absorbed by the atmosphere. If the concentration of greenhouse gases increases, more heat will be absorbed. The temperature of the atmosphere will increase. As a result, the rate of evaporation will increase from land and ocean, the water cycle will change, the humidity will increase and the climate will change. 3. Volcanic activities Volcanic eruption brings out tremendous amount of carbon dioxide, sulphur dioxide, water vapour, ashes and dust particles. These substances released in the atmosphere produce various other compounds that surround the earth’s atmosphere. If these substances are carried by equatorial winds, they will prevent the heating effect and thus cause cooling of climate.

150 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 151B. Human induced causes of climate changeSome human activities are also responsible for climate change. 1. Excessive carbon emission The emission of large amount of CO2 from burning of fossil fuels, coal, wood, respiration, etc. contributes to greenhouse effect due to which the overall temperature of the earth is increasing that results in climate change.2. Increasing temperature of the earthThe emission of large amount of greenhouse gases increases the overall temperature of the earth called global warming. The global warming causes the change in rainfall, snow fall, seasonal patterns, etc. As a result, it causes climate change.3. Ozone layer depletion The ozone layer prevents most of the solar radiation from entering. If the ozone layer becomes thinner due to CFCs, more amount of solar radiation enters the earth. The solar radiation that has entered the troposphere is absorbed by the earth's surface, water vapour, greenhouse gases etc. The remaining solar radiation escapes into the space. This absorbed solar radiation releases heat and increases the temperature of the earth. Then the climate of the earth changes. Most glacial lakes are flooding and possess the risk of a glacial lake outburst flood due to climate change. Water from the melting ice is a source of water for glacial lakes. The temperature of the country is increasing every year due to climate change. Ice is melting faster than usual. A huge quantity of water is entering the glacial lakes. So, most glacial lakes are at the risk of breaking and flooding. FACTS WITH REASONS4. Industrialization Industrialization increases industrial gases like the oxides of nitrogen and sulphur. They significantly alter climate due to their ability to reflect or absorb solar radiation. Thus, over a long period of time, this can cause climate change.5. Agricultural wastes, treatment of waste water and chemical fertilizers Agricultural waste such as hay, straw, husk etc. are degradable substances. They release carbon dioxide and methane gas during decomposition. It increases the level of greenhouse gases in the atmosphere. The higher amount of greenhouse gases absorbs the higher amount of heat from sunlight and raises the temperature of the earth. Hence, the climate will change. Similarly, the excessive use of chemical fertilizers has also increased the levels of nitrous oxide in the atmosphere which also contributes to global warming. After a long time, this causes climate change.6. DeforestationThe forest is lost to residences, agriculture, furniture, forest fires or landslides every year. If the forest is lost carbon dioxide won’t be absorbed from the air, carbon dioxide will increase in the air, the weather will be extreme, the temperature will rise, the water cycle will be

150 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 151disturbed, water resources will dry and carbon dioxide trapped in land and rocks will be released. Global warming will occur which will start climate change. Volcano causes climate change. Give reason.Regular eruption of volcano releases additional amount of green house gases including carbon dioxide in the atmosphere. These green house gases promotes global warming and cause climate change. FACTS WITH REASONSEffects of Climate ChangeClimate change has a direct and indirect effect on human health, weather, agriculture, the environment, the economy, biodiversity, water resources and other aspects. a. Impact on human healthClimate change can affect our health in different ways. Breathing problems may get worse because the air becomes more polluted and filled with things that can make us sick. Skin allergies might increase because of the weather changes. It can also make people feel more stressed and upset because things around us are changing. Sometimes, there might not be enough food to eat because the weather changes how we grow our food. Lastly, climate change can help bugs like mosquitoes and flies spread more easily, causing sickness that can spread to a lot of people, like a pandemic. b. Impact on weather and environment Climate change can disturb the weather and our surroundings. The water cycle becomes unpredictable. It gets super-hot sometimes, way more than usual. Storms happen more often. The weather becomes hard to guess. It might rain when it's not supposed to or be too warm when it should be cold. All these changes can make life tough for animals and plants because the temperatures aren't right for them. c. Decrease in agricultural production Agricultural production will decrease significantly. Due to climate change temperature of a place changes. Traditional crops grown in that region for many ages cannot grow well now. There is a lack of water for irrigation. New germs and diseases infect and damage the crops. Drought and flood destroys many crops and plants each year. Many plants die because of heat stress. Bacteria and fungi are more active in hotter climates. These organisms will also attack the crops, fruits and vegetables. Climate change decreases agricultural production. d. Impact on economyClimate can hurt the world economy. Since the climate is changing, the season might be disturbed. Seasonal tourism and ecotourism will decline. Agricultural production will decline. There will be fewer resources for forest and agriculture-based industries. Unemployment will increase. An energy crisis occurs due to the lesser production of electricity. e. Loss of biodiversityWeather patterns, seasons, water cycle, rainfall etc. are disturbed because of climate change. The weather is very hot, there is a lack of water, grass does not grow well, and

152 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 153diseases spread faster. As a result, many organisms cannot reproduce properly. They are dying or migrating to another place. So, biodiversity is lost in that place.f. Lack of water for drinking and irrigation Climate change has disturbed weather patterns, wind patterns, water cycle, average temperature etc. Since the monsoon is short and it brings very little rain, water is scarce. It does not snow much in winter either. There is very little snow in the mountains. In summer they melt faster than they should. So, mountain regions lose water faster in summer. As a result, there will be very little water during other seasons. g. Drought and floodClimate change and global warming have adverse effects in Nepal as well. The temperature of Nepal is increasing by 0.06°C each year due to over greenhouse effect. As a result, it does not rain or snow enough in the Himalayan region. The snow in the mountains melts faster than before. As a result, water is less in the Himalayan region and hilly region. All the water that melts from mountains and glacial lake outbursts floods. The water that did not change into snow in winter in the mountains causes flood in Terai. h. Rise of sea levelClimate change is real and the over-greenhouse effect has significantly increased the average temperature of the earth (global warming). The aftermath of this disaster is that the ice caps in the mountains, snow from the colder countries and the ice caps from the poles of the earth melting at an alarming rate and mixing into the ocean. More than that the continuous increase in the average temperature of the ocean will increase its volume as well. As a result, the sea level rises each year. Measures of climate change control and managementi. Rules and regulations Environment Conservation Act 2076 has directed the Nepal government, local government, private sector and province administration should plan and implement activities to reduce climate change and adapt to climate change. ii. Reduce carbon emissionsAlternative sources of energy such as electricity and solar are being used more in Nepal nowadays. The available source of energy should be used wisely and efficiently. Wind energy, biogas, briquette etc. is encouraged in the village. Improved fireplaces are being made in villages. Farmers should not burn agricultural waste. All these activities help to reduce the use of fossil fuels. Less carbon dioxide will be produced. iii. Carbon sequestrationThe process of removing carbon from the atmosphere is called carbon sequestration. We can plant more trees on barren land. Afforestation is the best way to reduce carbon dioxide from the air. We should prevent forest fires, timber smuggling and overgrazing. These activities will save plants. Then trees will absorb carbon dioxide from the air.In Nepal, environment conservation act was implemented in 2076 BS.MEMORY TIPS

152 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 153iv. Public awareness The government is and should be launching more programs to raise public awareness. People should be informed about climate change and its harmful effects. They should also be taught about how they can help to reduce climate change. For example, we can teach people that they should not burn plastic, should not use vehicles for short distances, should reduce the use of fossil fuels etc. Then they will change their behaviour and it will help to reduce climate change.Endangered animals and birds in Nepal Some animals and birds are large in number while some are less in a given geographical area. Animals or birds whose distribution is limited and are few in number at a given geographical area at that time are called endangered animals or birds. If the endangered animals and birds are not conserved in time, they may go extinct. Nepal has many species of endangered plants and animals. Causes of loss of biodiversity and extinction of plants and animals The major causes of the loss of biodiversity are weak rules, climate change, smuggling and poaching. Pollution, industrialization, growing random hybrid plants and keeping random pets without research. i. Climate change Weather patterns, seasons, water cycle, rainfall etc. are disturbed because of climate change. The weather is very hot, there is a lack of water, grass does not grow well, and diseases spread faster. As a result, many organisms cannot reproduce properly. They are dying or migrating to another place. So, biodiversity is lost in that place.ii. DeforestationWhen people cut trees, the climate will change. Then the ecosystem will be imbalanced. There will be a lack of food and shelter for organisms. So, their population will decrease. Many medicinal plants and rare plants will be extinct due to deforestation. iii. Extreme use of biological resources, smuggling and poaching Some people are illegally and excessively collecting medicinal plants, medicinal herbs, timber and precious trees and smuggling them out of the country. Some of them are also hunting rare and protected animals like elephants, rhinoceros etc. They kill it to sell the body parts of these animals. So, many plants and animals are becoming extinct. iv. Pollution due to industrialization and urbanization Modernization has increased pollution in the country. Many industries and factories are running in the countries. They use fossil fuels. They produce smoke and many solid wastes. People in the cities use vehicles, gas stoves etc. It also produces smoke. Tons of solid and liquid waste are produced from the city. When these solid, liquid and gaseous wastes mix in the environment, they make the environment toxic. Many animals and plants die due to this. v. Imported and hybrid organismsPeople bring many hybrid organisms and unique organisms from different parts of the world to the local community without proper research. Those plants and animals can disturb the local ecosystem. Then the original plants and animals will go extinct.

154 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 155Protected areas and protected species The plants, animals and birds that are banned by the law to harm or destroy are called protected species. The huge area separated by the government for the conservation of endangered species is called a protected area. Most of the protected animals are in protected areas. It is illegal and punishable by law to hunt or cut any protected species. 27 species of mammals, 9 species of birds, 3 species of reptiles and a few plants are declared protected species in Nepal. Some protected plants of Nepal: Launth salla, Golden Michelia, Sarpaghanda, Panchaunle, Jatamasi etc.Some protected mammals are: Pygmy Hog, Red Panda, Black Buck, Gaur Bison, Wild Yak, Wild Water Buffalo, Grey Wolf, Hispid Hare, Swamp Deer, Asiatic wild Elephant, Lynx, Stripped Hyaena, Asamese Monkey, Indian Pangolin, Chinese Pangolin, Himalayan Muskdeer, Clouded Leopard, Great Tibetan Sheep, Bengal Tiger, Snow Leopard, Tibetan Antelope, Gangetic Dolphin, Leopard Cat, Spotted Lingsang, One-horned Rhinoceros, Four Horned Antelope, Brown Bear, etc.Some protected birds are: Great-horned Hornbill, Cheer Pheasant, White Stork, Black Stork, Sarus Crane, Bengal Florican, Impeyan Pheasant, Lesser florican, Crimpson horned Pheasant, etc.Some protected reptiles are: Gharial, Asiatic rock python, Golden monitor lizard, etc.ACTIVITY 1Visit a nearby protected area. Observe different animals and birds in the area. Consult your teacher and find at least two protected mammals and two protected birds of that park. Describe them briefly mentioning their scientific names, body structure, food, life span and habitat with their figure. Conservation of endangered species of animals and birdsIt is necessary to conserve wildlife, endangered plants and animals because they are inseparable members of the vast ecosystem. Their extinction will hurt us in many ways. It will greatly disturb the food chain. The imbalance in the ecosystem causes suffering for many species including us. They are also a huge source of medicinal products, cosmetic products and attractions for tourists. Therefore, they must be conserved. Some ways to conserve them are discussed below. i. Study and research We should study and research habits, habitats, nature, lifecycle and other aspects of endangered species of plants and animals. If we understand their habit and habitat, we can prevent their extinction. ii. In-situ and ex-situ conservationThe process of conservation of organisms in their natural habitat is called in-situ conservation. For example, protecting Bengal tigers in national parks. The process of conservation of organisms outside their natural habitat or in manmade habitat is called ex-situ conservation. For example, protecting tigers in zoos or research labs. We can protect endangered species of animals in natural habitat (in-situ) or manmade artificial habitat (ex-situ).

154 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 155iii. Prevent poaching and smuggling of endangered animals Control of International Trade of Endangered Wild Fauna and Flora Act 2073 of the constitution of Nepal prohibits poaching and smuggling of endangered species. Local authorities should strictly work to prevent poaching and smuggling of endangered species. iv. Strict rules and regulationsThe poachers and smugglers should be punished according to the law of the country if found guilty. The rules and regulations should be strict. v. Conservation of habitat Conservation of habitat prevents wildlife from being extinct because if we conserve habitat then there will be shelter for wildlife. They can be safe from extreme weather and predators. There will be sufficient food for them. If there is sufficient food they will thrive in the forest. Conservation of the habitat of endangered animals conserves the ecosystem as well. Wildlife can survive well in a balanced environment.vi. Public participation Public participation is very important to prevent the extinction of endangered species because the people themselves are aware of the importance of endangered animals. They will stop hunting endangered animals and selling endangered plants. People will themselves protect, manage and harvest endangered and medicinal plants. People will make rules, find a budget, protect the forest and also use forest resources. This kind of activity will protect the forest. Some traditionally used medicinal plantsIntroduction to Medicinal plantsNepal is richer in biodiversity because of its unique geographical and physical properties. Its height ranges from 60 meters to 8848 meters. The temperature varies accordingly with altitude. Various landforms, water bodies and climate are available here. It results in 181 types of ecosystems. The plants whose various parts are used in traditional medicine are called medicinal plants. The use of medicinal plants is good for us because they have lesser amounts of chemicals. They have very less or no side effects at all. Herbal medicines (Ayurvedic medicines) are good for us because they have fewer side effects and help us to cure multiple diseases. Despite being commonly available, medicinal herbs are not processed into medicines because of lack of research, investment and market. They are also not popular among the patients. After all, they are expensive, less effective and slower in action. Medicinal plants have been discovered and used in traditional medicine practices since prehistoric times. Plants produce hundreds of chemical compounds for functions including defence against insects and fungal diseases. Out of 7000 flowering plants present in Nepal, more than 700 plants are used in medicines. Most medicinal plants are found in the Karnali region. Some of them are discussed below:

156 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 157Holy basil (Ocimum tenuiflorum)Holy basil, also known as Ocimum tenuiflorum, can grow in many different climates, except really cold places. Holy basil is a small annual or perennial shrub with a fragrant leaf. It's like a small herb with short, broad leaves that smell nice. People use the leaves of this plant to make medicine for things like breathing problems and sore throats. Tulsi (holy basil) is used to purify water and rinse the mouth due to its natural antibacterial and antimicrobial properties. Tulsi has antimicrobial properties. So, it can kill germs in our mouth, throat and stomach. It can improve digestion, cure throat pain etc. Tulsi is used as a biopesticide because of its antimicrobial properties. It can chase and kill pests. It is also used for making green tea. It removes impurities of air and supplies a greater amount of oxygen. Aloevera (Aloe vera)Aloevera scientifically called Aloe vera grows in subtropical climates, Terai, mid-hills, and nurseries. It is a succulent plant recognized by its thick, fleshy, and serrated stems. The medicinal properties lie in the gel inside its leaves, which acts like a natural remedy for skin irritations, burns and pimples and works as a sunscreen. Ghiukumari (Aloe vera) is a xerophyte with fleshy leaves and thorns. It is grown for its gel and juice. It is rich in vitamins A and C. Gel of aloe vera is used as sunscreen because it has chemicals which block sun rays, and prevents tanning. It is used as a moisturiser because it can retain water in the skin and prevent drying. Aloe vera is ayurvedically called Sanjivani because it has been used since ancient times for the treatment of diseases. Flagroot or Bojho (Acorus calamus)Calamus, scientifically known as Acorus calamus, is a perennial herb that is commonly found in marshlands, swamps, and pond banks, especially in the Terai and hills. It's an herb with sword-like leaves and an upright appearance, and its roots have a pleasant aroma. People use the rhizome, which is an underground stem, to make medicine. Bojho is a natural remedy that helps with throat problems and can even soothe an upset stomach. We will get nosebleeds if we consume excessive calamus. Asiatic pennywort (Centela asiatic)Asiatic pennywort, scientifically known as Centella asiatica, grows in tropical regions. It grows in moist and shady places such as swamps, paddy fields, lakes etc. Holy basilAloeveraFlagrootAsiatic pennywort

156 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 157Ghod tapre is a perennial herb with leaves that are shaped like kidneys and smell nice. Every part of this plant is useful for different things. It is also used to make skin toner and skin care cream. The fresh flowers are used to treat burns and wounds, and a paste made from it can help cure skin diseases. It is grown because it has antioxidant, antimicrobial properties and neuroprotective functions. Asiatic pennywort helps to reduce depression and anxiety and boosts memory. It can treat the common cold. Mugwort (Artemisia vulgaris)Mug wort, scientifically known as Artemisia vulgaris, is a medicinal shrub that grows in the mid-hilly regions. Tite paati is an aromatic herbaceous plant. People use the leaves of this plant to create cosmetic products and scented oils. So, mugwort is like a natural ingredient that adds a lovely fragrance to beauty products and oils. It is also used as a pesticide to chase insects, preserve food and as compost manure. Heart-leaved moonseed (Tinospora cordifoli)The Heart-leaved moonseed scientifically called Tinospora cordifolia, grows in nurseries and forests, especially in the terai and mid-hills. Gurjo is a climbing plant or shrub that spreads through its stems (vegetative propagation by stem). People use the stem and root of this plant to make medicine that helps make your immune system stronger, prevent infection and work as an antioxidant to reduce the chance of heart attack and certain cancers. Heartleaved moonseed is good for sugar patients because it can significantly lower blood sugar. However, overconsumption can be fatal to health because it can cause low blood sugar. Malabar Nut (Adhatoda vasica)The Malabar nut, scientifically known as Adhatoda vasica, is a medicinal plant that grows in the Chure range and Mahabharat range. Asuro is a medium-sized shrub. Vascinine, vasicinone and hydroxyl vasicine found in Malabar nut help to treat respiratory diseases by widening bronchioles. People use different parts of this plant for medicine. The leaves are used to treat problems with gums and teeth, while the flowers can help cure infections in the urine. The juice of the flower and leaf of the Malabar nut is used to relax bronchioles and remove mucus from the throat. It can be also used as a tea to treat the common cold. It is also used for composting. MugwortHeart-leaved moonseedMalabar Nut

158 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 159Neem (Azadirachta indica)Neem, scientifically known as Azadirachta indica, grows in places like the Terai region and mid-hill areas. It's a tree with small leaves and tiny white flowers that smell good. People use different parts of the neem tree, like the leaves, bark, and oil, to make medicine. It's great for treating skin problems, and neem juice can even help lower blood pressure, reduce bad cholesterol and purify blood. Neem is a multi-use plant because it is antimicrobial. Its various parts can be effectively used as bio-pesticides, natural food preservatives, and ointment to cure skin diseases such as chicken pox. Neem juice can also be consumed to lower bad cholesterol. High blood pressure patients drink neem juice because neem juice can decrease blood pressure and cause dizziness. Yarsagumba or Chinese caterpillar fungus(Cordyceps sinensis)Yarshagumba is an endangered species. Caterpillar fungus, scientifically known as Cordyceps sinensis, is found in the snow-covered grasslands of the tundra region, way up high at heights between 3000 m to 5000 m. It is a parasitic fungus that grows on a caterpillar. It has a long and white appearance. Yarshagumba is used as a source of energy, to improve stamina, to improve respiratory health etc. Its average length is 5 centimetres to 8 centimetres. Sporulation is asexual mode of reproduction of yarshagumba. Matured Yarshagumba releases its spores into the air. If it lands in the caterpillar, it produces hyphae and roots into the caterpillar. It is a parasite so it eventually kills the caterpillar. The dead caterpillar decays and becomes a source of nutrients for the fungus. Then the fungus grows into it and changes into Yarshagumba. The lower part is made of a caterpillar and the upper part is made of the fungus. It is collected by licenced locals when the snow melts in spring. If yarshagumba is protected and if its production is increased then the economy of the country will be improved because yarshagumba sells at a very good price. Local people can earn their livelihood by collecting and selling it. Ayurvedic medicines can be made from it and sold. They will pay taxes and the revenue of the country will increase. The collection, distribution and export of yarshagumba are controlled by the government because it is an endangered species. Without proper supervision, it might go extinct. Turmeric (Curcuma longa)Turmeric, scientifically known as Curcuma longa, is found in places like the Terai, mid-hills, and high hills. Beshar is an herb with a special underground stem called a rhizome and long, narrow leaves that stay green all year. People use the rhizome of this plant to make medicine. It's like a natural remedy that helps with skin issues, gets rid of toxins, and even prevents problems NeemYarsagumbaTurmeric

158 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 159with breathing and the heart. It is a perennial herb rich in curcumin, vitamins A, B, B2, C, phosphorus, iron and calcium. Turmeric is pasted on the skin to treat leprosy because of its antimicrobial and anti-inflammatory properties. Turmeric is used as an antimicrobial, as spices, to sterilize meat, to treat skin diseases leprosy and luto, to improve the health of lungs and hearts, and as a natural food colour and cosmetics. Conservation of endangered species of plantsi. Conservation of natural habitatsPlants survive in particular temperatures, humidity, water, weather and climate. Therefore, we must protect the natural habitats of the endangered plants so that they will not die. ii. Public awareness People should be taught to identify endangered species. If they can identify it, they will not unknowingly cut it while collecting fodder. They will protect it from grazing animals. They should be requested to not cut but to protect the plant. They should be informed that these plants are valuable, endangered and protected species. iv. Tissue culture Tissue culture is a modern technology. It can produce thousands of new saplings of endangered plants at once. Those plants can be planted and grown in suitable habitat to increase the population of these plants. v. Strict rules and regulations to prevent smuggling and illegal collection The rules and regulations should be strict and they should be implemented strictly to reduce the chances of illegal collection and smuggling of rare plants. vi. Public participation in medicinal use of rare plant species conservationPublic participation is very important to prevent the extinction of endangered species because the people themselves are aware of the importance of endangered species. They will stop selling endangered plants. People will themselves protect, manage and harvest endangered and medicinal plants. People will make rules, find a budget, protect the forest and also use forest resources. This kind of activity will protect the forest. Therefore, local people should be trained to identify, grow, protect, harvest and process medicines from rare plants. HOT SKILL HIGHER ORDER THINKING SKILL1. If you were the prime minister of Nepal, how would you minimize the effects of climate change in the country? Write in four points. If I were the prime minister of Nepal, I would do the following things:i. promote alternative sources of energy in place of fossil fuels. ii. encourage afforestation in every possible barren land. iii. encourage the farmers to use organic fertilizers in place of chemical fertilizers.iv. launch public awareness programmes extensively about climate change and its effects.

160 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 1612. Nepal is sensitive to climate change effects. Nepal has a wide range of vegetation, altitude and wildlife with socio-economic differences. It is fully dependent on climate. It is also rich in various medicinal plants, herbs, rare organisms and climatic features. The climate varies drastically just over a few kilometres apart. The temperature in Nepal has increased by 0.06°C due to various greenhouse gases and pollutants emitted globally. The water sources like the rivers, rivulets and springs have dried up. The flow volume of rivers has also decreased. Likewise, incidents of glacial lake outburst floods (GLOF) have also increased. Many organisms have gone endangered and even extinct. Moreover, the snow in the Himalayas is melting rapidly. Due to these various reasons, we can conclude that Nepal is sensitive to climate change effects. 3. Despite there are many medicinal plants in the forest of Nepal, people are using synthetic medicines. Even though different types of medicinal herbs are available, we still depend upon synthetic medicines to cure simple illnesses (ailments) because:i. We do not know how to harvest and use medicinal herbs but synthetic medicine is easy to use.ii. Medicinal herbs take time to work but synthetic medicines work fast.iii. Synthetic medicines are more easily available than medicinal herbs.4. Compare between endangered plants and medicinal plants. The comparision between endangered plants and medicinal plants are:SN Endangered plants SN Medicinal plants 1 The plants which are on the verge of extinction are called endangered plants. 1 The plants whose parts are used for medicinal practice are called medicinal plants.2 Endangered plants cannot be harvested. 2 Medicinal plants are farmed and harvested. 3. Endangered species are not common. Their population is too few.3. Medicinal plants could be common species or they could be endangered too.5. 'The main cause of climate change is air pollution.' Justify this statement. The mixing of harmful gases, dust and germs in the air is called air pollution. Air pollution is the leading cause of climate change because the polluted air contains large amounts of industrial gases, water vapour, methane, carbon dioxide gas etc. These gases trap solar energy and increase the temperature of the earth. An increase in the temperature of the earth will disturb the water cycle, direction of wind, ecosystem, rainfall etc. Then the climate will change. 6. Study the given diagram and answer the following questions. i. What is the scientific name of the plant? Ans: Scientific name: Ocimum tenuiflorum ii. What is the use of this plant in medicine? Ans: Tulsi is used for curing throat pain, colds, infections etc. iii. Tulsi is called a life-giving plant.Ans: Tulsi is called a life-giving plant because it gives a large amount of oxygen, remove toxin from the surrounding air and also helps to kill microbes, treat throat pain, prevent infection and improve digestion.

160 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 1617. Natural greenhouse effect is very essential on the earth.The natural greenhouse effect is very essential on the earth because:i. It helps to maintain the particular temperature of the earth’s surface in which living things can survive.ii. Greenhouse gases block most harmful solar radiation.iii. It maintains the weather and climate of the place. 8. Increase in the release of various greenhouse gases is the main cause of climate change. Greenhouse gases are those that can trap solar radiation and effect the weather of a place. If the quantity of greenhouse gases increases in the atmosphere, more quantity of solar radiation will be absorbed by the atmosphere. As a result, the average temperature of the earth will increase. It can disturb the weather and water cycle. Ultimately it can change the climate of a place. 9. Climate change would not occur if there were no existence of human beings on the earth. Explain. Climate change is a natural process. However, climate change would not be this fast if there were no humans in the earth because:i. No humans no use of fossil fuelHumans use LPG for kitchens, petroleum for vehicles and coal for industries. It releases large amounts of carbon dioxide which changes the climate. If there were no humans no one would use fossil fuel. ii. No agriculture no greenhouse gasesGreenhouse gases cause climate change. The use of chemicals, decomposition of agricultural waste, burning of husks etc. releases greenhouse gases such as methane and carbon dioxide gas in the air. iii. No industries no industrial gasesIf there were no humans, there would not be industries. No smoke would be mixed in the air.iv. No human no deforestation If there were no humans, no forest would be lost to residences, agricultural, industrial areas, forest-based industries etc. There would be more trees. Carbon dioxide would be absorbed by the forest. There would be no climate change. Hence, if there were no humans, there would not be deforestation, industries, or agriculture and no one would use fossil fuel. Greenhouse gases would not be produced. Then the climate would not change much. 4 STEPS EXERCISE EXERCISESTEP11. Multiple Choice Questions a. Which plant is used for its properties such as antioxidant, antimicrobial and neuroprotective functions? i. asiatic pennyworth ii. mugwort iii. aloevera iv. yarshagumba b. What greenhouse gases can do?i. trap heat from the earth and release it out of the atmosphere ii. trap heat from the sunlight and increase the temperature of the atmosphere

162 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 163iii. absorb heat from the atmosphere and decrease its temperature iv. maintain air pressure c. What is asuro (Malabar nut) used for?i. curing cough, cold and asthma ii. curing heart attack and cancer iii. treat gastrointestinal diseases iv. to make perfume d. Which group does the Holy Basil belong to?Medicinal value Endangered species Flora (plants) A BFauna (animals) C Di. A ii. Biii. C iv. De. Which one of the following is an effect of climate change?i. afforestation, carbon sequestration, clean energy ii. decrease in agricultural production, loss of biodiversity, irregular rainfall iii. fossil fuels, greenhouse gases, global warmingiv. tsunami, volcano and solar flares f. Which group does the Gangetic dolphin belong to? i. protected mammal, endangered species ii. friendly animal, aquatic animals iii. national animal, medicinal animal iv. endangered plants, rare plants g. Why should we reduce the use of fossil fuels? i. prevent global warming, prevent acid rain, prevent climate change, prevent health hazards ii. avoid heavy rainfall, avoid acid rain, lack of public awareness, avoid health hazards iii. afforestation, to use electricity, solar energy and biomass energy iv. to use petroleum, coal, diesel, keroseneh. Observe the given statement and arguments. Decide the correct and incorrect statements. Statement: It is punishable by law to kill one-horned rhinoceros in Nepal. Argument 1: It is protected under the Control of International Trade of Endangered Wild Fauna and Flora Act, 2073. Argument 2: We can kill it, if it is for medicinal purposes. i. Statement is correct. Both arguments are wrong. ii. Statement is incorrect. Both arguments are correct. iii. Statement and argument 1 are correct. Argument 2 is incorrect. iv. Argument 1 and argument 2 are correct. The statement is wrong.

162 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 163i. Identify the organism.Habitat Mode of reproduction Mode of nutrition Snow-covered grasslands Sporulation Parasitism i. snow leopard ii. chinese caterpillar fungus iii. golden michelia iv. himalayan muskdeer j. Which one of the following is a set of endangered birds? i. gharial, golden monitor lizard, Asiatic rock python ii. Indian pangolin, four-horned antelope, black buck iii. white stork, Bengal florican, crimson horned pheasant iv. launthsalla, champ, jatamasia. i b. ii c. i d. i e. ii f. i g. i h. iii i. ii j. iii Ans of MCQSTEP22. Very short questions a. Which one is called an extinct species between A and B? A B population is zeropopulation tends to zero Species b. Which plant is shown in the diagram? c. How can excessive greenhouse gases cause loss of biodiversity? d. What happens if the concentration of carbon dioxide is increased in the atmosphere?e. Write a difference between extinct species and endangered species. f. Why should we not consume excessive bojho?g. Give an example of each protected bird, protected mammal and protected reptile found in Nepal. h. Why is it necessary to conserve wildlife, endangered plants and animals?i. Nepal has a central zoo, where many animals are kept. Besides tourism,its role is the conservation of animals. What is this kind of conservation practice called?STEP33. Short questions a. Harkamaan is a local farmer. Irregular rainfall has ruined his crops. What is the main cause of this tragedy? What kind of activities could have led to this? b. The population of wild lives and plants are dropping significantly. Many of them are already endangered and some of them are extinct already. What kind of human activities led to this tragic result? c. Mr. Ram Bhakta puts fresh tulsi leaves in a cup of water for 20 minutes and then drinks it every day. Does it help to improve his health or is it just dogma? If it helps to improve his health, what does it actually do? Enlist.

164 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 PBd. Mr. Khadka has bought a new motorbike. He rides it to go to his office 2 kilometres away from his home. Is it wise to do so? How does it hurt the climate? What should he do? Suggest to him some right things to do to mitigate climate change regarding vehicles. e. What are the differences between the greenhouse effect and climate change?f. Despite the availability of medicinal herbs in our surroundings, we are dependent upon imported medicines. What could be the cause of this situation? What can we do to increase the use of medicinal herbs?g. Mrs. Khatri started a forest fire in a nearby village. She says it’s a good thing to do because new grass grows on the ashes of burnt forest next month where her goats can graze. Remind her how wrong is she to do that and also tell her how is it accelerating climate change. h. If you were the prime minister of Nepal, how would you minimize the effects of climate change in the country? STEP44. Long questions a. What type of plant is Malabar nut? Write its habitat. What is it used for? Does it have a side effect? What are they?)b. Climate change is one of the major causes of the loss of biodiversity in Nepal. Justify.c. Most glacial lakes are flooding and possess the risk of a glacial lake outburst flood. What has climate change to do with this problem?d. Mrs. Rama ground the aloe vera leaf and spread it over the burnt skin in her grandchild's hand. Does it help? What are the other uses of this medicinal plant? Discuss.e. Study given news published in Online Khabar, Wed, July 5, 2023 [3 Arrested for killing Rhinos][Chitwan National Park has arrested three people accused of killing two rhinos inside the national park. A 12-year-old female rhino and her four-year-old calf were killed using an electric trap. The three, Hom Bahadur BK, Krishna Bahadur Mahato and Shikharam Tharu, from Dharampur of Ramgram municipality 8 in Nawalparasi district were caught red-handed selling rhino horns, said the CNP chief conservation officer Dil Bahadur Pun. They were arrested on April 20.]Why is hunting of Rhinos illegal? How can we prevent the extinction of rhinos? ♦♦♦

PB <Running HeadeR> Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 165Key terms and terminologies of the unit1. Force: Force is a pull or push which changes or tends to change the state of rest or of uniform motion of a body in a straight line. 2. Gravitation: Force of attraction between two bodies in the universe due to their masses is called gravitation. 3. Law of gravitation: According to Newton's universal law of gravitation, 'Every body in the universe attracts every other body with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.' 4. Universal gravitational constant: Universal gravitational constant (G) is the gravitational force existing between two unit masses which are separated by a unit distance.5. Gravity : The force with which the heavenly bodies like planets, satellites, etc. pull the objects towards their centers is called gravity. 6. Acceleration due to gravity: The rate of change in velocity in a freely falling body under the effect of gravity only is called acceleration due to gravity. 7. Free fall: The condition in which an objects falls freely only due to the force of gravity , without any external resistance is called free fall.8. Mass: The total quantity of matter contained in a body is called mass. 9. Weight: The force with which the heavenly bodies like planets, satellites etc. attract a mass towards their center is called weight.10. Weightlessness: The condition in which the weight of an object becomes zero even if it has mass is called weightlessness. Sequence of Curriculum Issued by CDC Gravitational force: introduction, laws and simple mathematical expression Force of gravity: force of gravity and weight; acceleration due to gravity; relation between acceleration due to gravity, weight and mass; relation of acceleration due to gravity with the radius of the earth Free fall: Introduction; numerical using equation of linear motion  Introduction to falling of an object on the earth and its application in daily lifeUNITForce and Motion7Estimated teaching period Theory Practical8 2Yadav Pandit, hailing from Tikuri in Pyuthan District, Nepal, is a revered physicist renowned for his expertise in nuclear and heavy ion physics. Educated at Tribhuvan University and Kent State University, USA, Pandit's research has profoundly influenced our comprehension of atomic nuclei and subatomic particles. His ground-breaking contributions extend to practical domains such as nuclear energy and medical diagnostics, leaving a lasting impact on these fields. Yadav Pandit, About the Nepalese Scientist

166 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 167IntroductionForce is an external agent which tends to change the state of rest and state of motion of an object. Its SI unit is Newton (N) and its CGS unit is Dyne. There are various forces. Some of them are contact forces and some of them are non-contact forces. Some of them are pushing force and some of them are pulling force. The gravitation is a non-contact pulling force by nature. It exists because the matter has mass. Gravitation exists in any object that has mass. The earth, the moon, the sun, the stars, the galaxies and the black holes have gravity. Even tiny things such as grains of sand, dust, buildings, rocks, our body etc. also have gravity but too little. GravitationWe are familiar with the fact that an object thrown upward falls back to the earth surface, rain-drops from the clouds fall on the earth, the earth revolves around the sun, the moon revolves around the earth, etc. All these phenomena are due to the force of attraction between two masses.Celestial bodies have their orbit due to the force of attraction. In the second century, a Greek scientist, Claudius Ptolemy, proposed geocentric theory of the universe. According to this theory, the sun and other planets in the solar system revolve around the central earth. It continued for a long time. Nicolas Copernicus proposed the heliocentric theory in 16th century. According to this theory, the sun is at the center of the solar system and other planets revolve around it. Later, the great English physicist, Sir Isaac Newton, studied about the motion of the planets around the sun. FACTS WITH REASONSThe effect of gravitational pull is clearly visible in the liquid but not in the solid. The effect of gravitation is found to be seen more easily in liquids than in solids. For, example, the gravitation from the moon pulls tides in the ocean but does not pull tides in the land. It happens because the ocean is water. The liquid molecules are loosely arranged. They have weaker intermolecular forces. So, they move easily toward the moon due to gravitational pull. Hence, they form tides. However, on the other hand, the land is solid. The molecules of a solid are bound by strong intermolecular forces. So, they do not move easily, when pulled by the gravitational pull from the moon. So, the land does not form tides. Newton's Universal Law of GravitationSir Isaac Newton noticed that any object that has mass attracts another object that has mass. The mutual force of attraction between them that exists due to their masses is called gravitation. He also noticed that smaller things such as one building also exert F F SunEarthMoonGravitational pullGravitation between two objects is always constant if their masses and distance between them is kept constant. MEMORY TIPSAccording to Geocentric theory, earth is the centre of the solar system and the universe.MEMORY TIPSAccording to Heliocentric theory, the sun is the centre of the solar system and the universe.MEMORY TIPSEffect of gravitational pullEarthMoon High tideLow tideCombined gravitational pull of the sun and the moon

166 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 167gravitational force on another building. However, the gravitational force between them is not noticed because they are too small. Since they are small and have very less masses, the gravitation between them is also little. But in the case of the Earth and the moon, both objects are massive. They have a lot of mass. So, the gravitation between them is also noticeably greater. The gravitation between the Earth and the moon keeps the moon in its orbit. So, from this explanation, we can tell that the gravitation between two objects is directly proportional to the product of the masses of two objects. We know the fact that the sun is way too massive than the earth. However, the moon does not revolve around the sun but revolves around the earth. Why does this happen? It happens because the moon is way too far from the sun than it is from the Earth. Therefore, there is less gravitation between the sun and the moon. The Earth is very close to the moon. Therefore, there is more gravitation between the earth and the moon. So, from this explanation, we can tell that the gravitation grows weaker with an increase in distance. Mathematically, gravitation is inversely proportional to the square of distance between the centres of two objects. Hence, from these two observations, Newton proposed his popular hypothesis called Newton’s universal law of gravitation in 1687. Newton’s universal law of gravitation states that, “Everybody in the universe attracts every other body with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.” The gravitational force acts in the direction along the line joining the centres of the two bodies.Mathematically it takes the form,F ∝ m1m2 d2Where F is the gravitational force, G is the gravitational constant, m1 is the mass of the first object, m2 is the mass of the second object and d is the distance between the centres of these two objects. Newton's law of gravitation is valid for the force of attraction between any two bodies in the universe. Such two bodies are from tiny microscopic objects (atoms) to huge celestial objects like stars, planets, galaxies, etc. So, Newton's law of gravitation is called universal law.Suppose a body A of mass 'm1' and another body B of mass 'm2' are at a distance of 'd' from their centers. Distance between two masses (d) Gravitational force (F)Decreases by 2 times Increases by 4 timesIncreases by 2 times Decreases by 4 timesi.e. F ∝ 1d2

168 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 169Expression of Newton's Universal Law of GravitationNow, according to Newton's universal law of gravitation,The gravitational force (F) between body A and body B is directly proportional to the product of their masses.i.e. F ∝ m1m2 ………… (1) and;The gravitational force (F) between body A and body B is inversely proportional to the square of the distance between their centers.i.e. F ∝ 1d2 ………… (2)From the relation (1) and (2), we getF ∝ m1m2 d2or, F = Gm1m2 d2[Where G is a constant called universal gravitational constant. Its value is 6.67×10-11Nm2/kg2]The Universal Gravitational ConstantDefinitionConsider two unit masses separated by a unit distance, i.e. m1 = m2 = 1kg and d = 1mThen, the gravitational force between them,F = Gm1m2 d2 = G1 × 1 12 = GThe universal gravitational constant (G) is the gravitational force existing between two unit masses which are separated by a unit distance.Units of GG = F ×d2m1m2 Unit of G = unit of F × (unit of distance)2unit of mass × unit of mass = N × m2kg × kg = N m2 kg–2Thus, the SI unit of G is N m2 kg–2. In CGS system, the unit of G is dyne cm2 g-2.Value of GLong after Newton's death, the value of G was first determined experimentally by English physicist, Henry Cavendish (1731-1810) by using an extremely sensitive torsion balance in 1798 AD. In SI units, its value is 6.67×10-11Nm2/kg2.Properties of Gi. The value of G is independent of the nature of medium between two bodies. ii. The value of G is independent of the nature, size or masses of the bodies.iii. The value of G is unaffected by temperature and pressure.dAm1Bm2F = G1m1 kg 1 kg

168 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 169FACTS WITH REASONSThe gravitational constant is called a universal constant, why?The value of gravitational constant does not depend on the nature of the medium between two bodies. It also does not depend on masses of the bodies. The value of G is same for all pairs of objects, at all distances of separation. So, the gravitational constant is called a universal constant.Applications of Newton’s Law of GravitationNewton’s law of gravitation is applied in multiple fields. Some of them are:i. Calculation of mass of heavenly objects.ii. Hunt for habitable planets.iii. Predict the distance between galaxies.iv. Calculate the revolution duration of the planets. Solved Numerical 7.1Calculate the gravitational force between two students A and B having masses 50 kg and 60 kg, respectively, sitting at a distance of 10 m on a bench.Solution: Given mass of student A (m1) = 50 kg Mass of student B (m2) = 60 kg Distance (d) = 10 mWe have, F = Gm1m2 d2 = 6.67 × 10 –11 × 50 × 60102 = 20,010 × 10-11-2or, F = 2.001 × 10-13+4 = 2.001 × 10-9 NTherefore, the gravitational force between two students is 2.001 × 10-9 N.FACTS WITH REASONSThe moon cannot pull water from the Fewa Lake.The moon cannot pull water from the Fewa Lake because the mass of the Fewa Lake is less. The gravitation between two objects is directly proportional to the product of masses. F ∝ m1.m2. Since the mass of water in Fewa is less, there is less gravitation between the moon and the Fewa Lake. So, the moon cannot create tides in Fewa.Solved Numerical 7.2The mass of the earth is 6 × 1024 kg and that of the moon is 7.4 × 1022 kg. The distance between them is 3.84 × 105 km. Calculate the gravitational force between the earth and the moon.Solution: Given, Mass of the earth (m1) = 6 × 1024 kg Mass of the moon (m2) = 7.4 × 1022 kg Distance between the earth and the moon (d) = 3.84 × 105 km = 3.84 × 108 mThe gravitational force between big objects having very large mass is very strong in nature. Such a strong force of attraction between the earth and the moon binds them and makes the moon move around the earth.MEMORY TIPS

170 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 171We have,F = Gm1m2 d2 = 6.67 × 10 –11 × 6 × 1024 × 7.4 × 1022(3.84 × 108)2 = 296.148 × 1035 × 10–1614.745 = 2.008 × 1020 NTherefore, the gravitational force between the earth and the moon is 2.008 × 1020 N. Change in gravitational force due to variation in their masses and the distance between thema) Change in gravitational force between two bodies when their masses change but the distance between them remains constanti) When the mass of one object is doubledLet the mass of two objects be 'm1' and 'm2' and the distance between them be 'd'. According to Newton's universal law of gravitation, the gravitational force between two masses is given by F = Gm1m2 d2 ………………… (i) When m1 is replaced by 2 m1, then F' = G2m1m2 d2 = 2 Gm1m2 d2 From equation (i) F' = 2F Therefore, the gravitational force between two masses increases by two times when the mass of one object is doubled.ii) When the mass of both objects is doubledAccording to Newton's universal law of gravitation, the gravitational force between two masses is given by F = Gm1m2 d2 ………………… (i)When m1 is replaced by 2 m1 and m2 is replaced by 2 m2, then F' = G2m12m2 d2 = 4 Gm1m2 d2From equation (i)F' = 4F Therefore, the gravitational force between two masses increases by four times when the mass of both objects is doubled.dm1 m2d2m1m2dm1 m2d2m1 2m2

170 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 171b) Change in gravitational force between two bodies when their masses remain constant but the distance between them gets changedi) When the distance between two objects is reduced to halfLet the mass of two objects be 'm1' and 'm2' and the distance between them be 'd'. According to Newton's universal law of gravitation, the gravitational force between two masses is given by F = Gm1m2 d2 ………………… (i)When the distance between two objects is reduced to half, i.e. d is reduced to d2, then F' = Gm1m2 2 d2 = 4 Gm1m2 d2 From equation (i) F' = 4 F Therefore, the gravitational force between two masses increases by four times when the distance between them is reduced to half.ii) When the distance between the two objects is doubledAccording to Newton's universal law of gravitation, the gravitational force between two masses is given by F = Gm1m2 d2 ………………… (i)When the distance between two objects is doubled, i.e. increased from 'd' to '2d', thenF' = Gm1m2 (2d)2 From equation (i) F' = 14 F Therefore, the gravitational force between two masses decreases by four times when the distance between them is doubled.Consequences of the Gravitational ForceGravitation is a pulling force. Some consequences of gravitation are:i. The moon revolves around the Earth.The gravitation that exists between the Earth and the moon has aligned the moon in a fixed orbit around the earth. dm1 m2m1 m2d2dm1 m22dm1 m21. To revolve planets around the sun, the necessary centripetal force is provided from the sun.2. Due to difference in mass and distance from the sun, different planets have different velocity.MEMORY TIPS

172 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 173ii. Earth revolves around the sun.The gravitation that exists between the Earth and the sun has aligned the Earth in a fixed orbit around the sun.iii. Solar system exists.The mutual gravitation between satellites, dwarf planets, asteroids, planets and the sun has aligned every member of the solar system in their fixed orbits to form a solar system.iv. Constellation exists.The mutual gravitation between the stars of the constellation keeps them together so they maintain their shape. v. Formation of galaxies. The mutual gravitation between billions of stars and sometimes black holes between them pulls all of them together to form galaxies. vi. Determination of the future of the universe. The gravitation produced by the mean density of the universe determines the shape of the universe. If gravitation is stronger than the expansion force from the Big Bang, the universe will be close. If gravitation is weaker than the expansion force from the Big Bang, the universe will be open. If the gravitation equals to forces of expansion from the Big Bang, the universe will be flat.vii. Formation of stars. The gravitation shrinks the nebula into a hot ball of gases. It further shrinks due to gravity and the fusion reaction starts. Then a star is formed.viii. Tides rise in the ocean, especially during the full moon and new moon. The gravitation between the moon and the massive water body of the ocean is great. Due to this, the tides originate in the ocean. During the full moon and new moon, the moon comes closer to the earth. Due to the decrease in distance, the gravitation grows stronger during the full moon and new moon. Hence, tides become taller and more frequent during the full moon and new moon. ix. Gravity exists due to gravitation. Gravity is a special case of gravitation. Gravity is gravitation when one of the objects is massive but another one is relatively very small. x. The same planet exerts different magnitudes of gravitation on different objects at different places from Earth.The same planet exerts different magnitudes of gravitation on different objects at different places from Earth because gravitation is a mutual attraction. The final value of gravitation between two objects depends upon the mass of the earth, the mass of that object and the distance between them.

172 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 173GravityIt is said that about the year 1665, at the early age of 23 years, Newton was sitting in his garden under an apple tree. An apple from the tree fell on him. After this observation, he thought for a long time and said that the earth exerts a force of attraction on the apple in downward direction. This force exerted by the earth on the apple is called gravity of the earth. Thus, the force with which the heavenly bodies like planets, satellites etc. pull the objects towards their centers is called gravity.For example, objects falling towards the earth when released from a height is due to gravity. The SI unit of gravity is newton (N). It is a vector quantity. The gravity (F) of the earth or a planet depends on its mass (M) and radius (R). The gravity of a planet acts towards its center.The earth is like a giant spherical ball. People in the northern hemisphere as well as in the southern hemisphere stand upright. It becomes possible due to the earth's gravity which pulls all the objects towards its center. The gravity of a planet, or a heavenly body, can be calculated on the basis of Newton's law of gravitation.Gravity (F) = Weight (W) = GMmR2 [ ∵ F = W ]Where, F = Gravity, W = Weight of the body, M = Mass of the planet, m = Mass of the body, R = Radius of the planet and G = Gravitational constantDifferences between Gravitation and Gravity.Gravitation Gravity1. Gravitation is the force of attraction between two masses in the universe.1. Gravity is the force with which the heavenly bodies like the earth attract other smaller bodies towards their centers.2. The gravitational force between two masses' m1' and 'm2' separated by a distance 'd' is F = Gm1m2 d2 .2. The force of gravity on a body of mass 'm' is F = mg, where 'g' is acceleration due to gravity.Effects of gravityGravity is a special case of gravitation. Some effects of gravity are listed below:i. Objects, rainfall, hailstones, apples etc. fall toward the earth. Any objects such as pens, hailstones, apples, books, stones, fruits in the trees etc. are matter. They have mass. So, there must be gravitation between each of them and the earth. The gravity pulls all of them toward the centre of the earth. The gravity of the earth is about six times more than that of the moon. Thus, a body weighing 1 N on the moon weighs 6 N on the earth. Similarly, a man jumping 1 m on the earth can jump 6 m on the moon.Memory TipsGravityPhET interactive simulation website allows us to observe the variation of gravitation with variations in mass or distance on the internet.MEMORY TIPS

174 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 175ii. Acceleration is produced in a falling object.It is observed that whenever an object falls from its place, gravity pulls it and produces motion in it. The motion is not uniform. The velocity is increasing every second. Therefore, acceleration is produced in the falling object. Thus, produced acceleration is called acceleration due to gravity. iii. Atmosphere and ocean exist. The atmosphere is made of air and the ocean is made of water. The air and the water are made of matter. So, the force of gravity pulls them down and holds them on the surface of the earth. Hence, the layer of air called the atmosphere is formed and the layer of water called the hydrosphere is formed around the earth. iv. Object got weight. Gravity pulls everything on its surface downward toward the centre of the earth. This pulling force is also called weight. Hence, the gravity of the planet gives weight to an object. Gravity acting on an object equals the weight of the object. It is difficult to lift objects because it is a work against gravity. They have weight. We have to use force more than their weight in the opposite direction of gravity to lift stones. If an object is too far from the Earth, it is not affected by the gravity of the Earth and becomes weightless in space. v. Stability of buildings.The buildings can stand, we can stand and walk etc. because gravity is pulling us down. vi. Flowing of the river.The river water has mass. So, it is being continuously pulled by the gravity. As a result, the liquid flows toward a lower altitude up to the ocean. vii. Gravity can produce freefall in an object. When the gravity pulls objects downward, it accelerates. If no other external forces affect that falling object, then that object goes into the state of freefall. viii. Satellite revolves around the earth.The artificial satellites revolve around the Earth because they are continuously pulled down by the gravity of the Earth. They are in a state of freefall at a suitable distance with a suitable orbital velocity. Acceleration due to gravityForce applied on a moving body changes its velocity. While falling, the magnitude of the velocity of the object changes due to the earth's gravity. This change in velocity is responsible for acceleration. Thus, the rate of change in velocity in a freely falling body under the effect of gravity only is called acceleration due to gravity. It is denoted by 'g'. The unit of 'g' is the same as that of the acceleration, i.e. ms-2. Acceleration due to gravity is a vector quantity. The average value of acceleration due to gravity on the earth is 9.8 ms-2.FACTS WITH REASONSAcceleration due to gravity of the earth is 9.8 m s-2. What does it mean?Acceleration due to gravity of the earth is 9.8 m s-2 which means, when an object is falling freely under the influence of the earth's gravity, its velocity increases at the rate of 9.8 m/s per every second.

174 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 175ACTIVITY 1Use a stop watch, marble and measuring tape to calculate the value of acceleration due to gravity. (Note: Do it under the guidance of your teacher or guardians to avoid any accident.)1. Measure the height of the roof of your building with the help of a measuring tape. 2. Drop a marble from the roof. As you drop the marble, say start to your friend to press the stop watch.3. Tell your friend to stop the watch when he/she listens the sound of hitting the ground.4. Repeat this procedure 10 times and record the data of the time taken. 5. Use the liner equation of motion, h = ut + 12 gt2 to calculate the value of acceleration due to gravity in each case. When u= 0, h = 12 gt2. Finally take the average of all the 10 measured values of 'g'. This gives the acceleration due to gravity.Derivation of the expression for acceleration due to gravity, g = GMR2Let an object of mass 'm' be present on the surface of the earth having mass 'M' and radius 'R'. According to Newton's universal law of gravitation, the gravitational force 'F' between the object and the earth is given by the formulaF = GMmR2 ………………… (i)According to Newton's second law of motion, force is the product of mass and acceleration. So, the magnitude of the gravitational force on the body of mass 'm' is given by the product of its mass and acceleration due to gravity. i.e. F = mg ………………… (ii)From equation (i) and (ii)mg = GMmR2 or, g = GMR2From this equation, the value of acceleration due to gravity 'g' is independent of the mass, shape and size of the body. Solved Numerical 7.3The mass of the earth is 6 ×1024 kg and its radius is 6400 km. Calculate the value of acceleration due to gravity on the surface of the earth.Solution: Given, Mass of the earth (M) = 6 ×1024 kg Radius of the earth (R) = 6400 km = 6400 × 1000 m = 6.4 ×106 mWe have, g = GMR2or, g = 6.67 × 10 –11 × 6 × 1024(6.4 × 106)2 = 40.02 × 1024 – 1140.96 × 1012 = 9.8m/s2RMEarthmThe value of acceleration due to gravity 'g' does not depend upon the mass of the falling body 'm'. But, it depends upon the mass and radius of the planet.MEMORY TIPS

176 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 177Solved Numerical 7.4Mass of the moon is 7.4 × 1022 kg and its radius is 1740 km. Calculate the value of acceleration due to gravity on the surface of the moon.Solution: Given, Mass of the moon (M) = 7.4 × 1022 kg Radius of the moon (R) = 1740 km = 1740 × 1000 m = 1.74×106mNow, the acceleration due to gravity 'g' is calculated by the formula g = GMR2 = 6.67 × 10 –11 × 7.4 × 1022(1.74 × 106)2 = 49.358 × 10113.028 × 1012 = 1.63m/s2Solved Numerical 7.5The mass of the Jupiter is 319 times heavier than the mass of the earth and its radius is 11 times longer than that of the earth. Find the value of acceleration due to gravity of the Jupiter.Solution: Given, Me is the mass of the earth and Re is the radius of the earth Mass of the Jupiter (MJ) = 319 Me Radius of the Jupiter (RJ) = 11 ReThe acceleration due to gravity of the Jupiter gJ = GJMJRJ2 = G319Me(11Re)2 = 319GMe121Re2 = 2.636 × ge = 2.636 × 9.8 [GMeRe2 = g = 9.8 m/s2]or, gJ = 25.83 m/s2FACTS WITH REASONSThe mass of the Jupiter is about 319 times heavier than that of the earth but its acceleration due to gravity is only about 2.636 times` greater than that of the earth, why?The acceleration due to gravity of a planet having its mass 'M' and radius 'R' is given by g = GMR2 . It means g ∝ 1R2 . Eventhough the mass of the Jupiter is so much heavier than that of the earth, the square of its radius reduces the value of acceleration due to gravity. Thus, the mass of the Jupiter is about 319 times heavier than that of the earth, but its acceleration due to gravity is only about 2.636 times greater than that of the earth.Differences between acceleration due to gravity (g) and universal gravitational constant (G).Acceleration due to gravity (g) Universal gravitational constant (G)1. The rate of change in velocity of a freely falling body due to gravity is called acceleration due to gravity.1. Universal gravitational constant (G) is the gravitational force existsing between two unit masses which are separated by a unit distance.

176 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 1772. The value of 'g' varies from place to place on the earth. 2. The value of G is constant i.e. 6.67×10-11Nm2kg-2.3. 'g' is a vector quantity. 3. 'G' is a scalar quantity.Variation of 'g' on the earthAcceleration due to gravity (g) is inversely proportional to the square of the radius of the earth. As we know the earth is not completely spherical, the value of the earth’s radius changes from place to place. Hence, acceleration due to gravity also changes from place to place. So, it is not the same in all parts of the surface of the earth. However, the value of ‘g’ is the maximum on the surface of the earth. The value of acceleration due to gravity also varies with altitude from the surface of the earth and with the depth from the surface of the earth. a) Variation of 'g' on the surface of the earthThe acceleration due to gravity is given by the formula,g = GMR2Where, G is a constant and M is also a constant quantity for heavenly bodies like planets, satellites etc. So, acceleration due to gravity on the surface of a planet like the earth depends upon its radius. The acceleration due to gravity of the earth is inversely proportional to the square of its radius. i.e. g ∝ 1R2Earth is not a perfect sphere. The radius at the equator is greater than the radius at pole, i.e. Re > Rp. The radius of the earth is maximum at the equator, so the value of 'g' is minimum at the equator (ge = 9.78 m/s2). Similarly, the radius of the earth is minimum at the poles. So, the value of acceleration due to gravity is maximum at poles (gp = 9.83 m/s2). The value of acceleration due to gravity increases when we go from the equator to the pole. b) Variation of 'g' with heightThe acceleration due to gravity at height 'h' from the earth surface is given byg' = GM(R + h)2Where 'M' is the mass of the earth and 'R' is its radius.The value of acceleration due to gravity decreases with the increase in height from the earth surface.Solved Numerical 7.6Mass of the earth is 5.972 × 1024 kg and its radius is 6371 km. Calculate the value of acceleration due to gravity acting on a satellite at the height of 3772 km from the surface of the earth. Also, calculate the weight of that satellite if its mass is 3,238 kilograms. Solution: Given, Mass of the earth (M) = 5.972 × 1024 kgR moreR lessR moreEarthPole (g=9.83 m/s2)Equator(g=9.78 m/s2)RhEarthmRelation between g and g'g = GMR2 ........ (i)g' = GM(R + h)2 ........ (ii)g'g = GM(R + h)2 ÷ GMR2 = GM(R + h)2 × R2GMg' = R2(R + h)2 × gMEMORY TIPS

178 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 179 Radius of the earth (R) = 6371 km = 6371000 m Height of the satellite (h) = 3772 km = 3772000 mRadius + height (R+h) = 6371000 + 3772000 = 10143000 meters Acceleration due to gravity (g) =?Using formula, g' = GM(R + h)2 = 6.67 × 10–11 × 5.972 × 1024(10143000)2 = 6.67 × 10–11 × 5.972 × 1024 × 10111.0288 × 1014 = 39.83324 × 10131.0288 × 1014 = = 38.717 × 10-1 = 3.87 m/s2Again, Mass of satellite (m) = 3,238 kgAcceleration due to gravity acting on the satellite = 3.87 m/s2Weight of satellite =?Now, Weight of satellite = mass of satellite x acceleration due to gravity acting on the satellite = 3,238 × 3.87 = 12,531.06 NFACTS WITH REASONSThe value of acceleration due to gravity is less at the top of Mt. Everest than that in the Terai region, why?The acceleration due to gravity at height 'h' from the earth surface is given by g' = GM(R + h)2 . It means g' ∝ 1(R + h)2When height 'h' from the sea level increases, the value of acceleration due to gravity decreases. Height 'h' at Mt. Everest is more than that in the Terai in our country. So the value of acceleration due to gravity is less at the top of Mt. Everest than that in the terai region.c) Variation of 'g 'with depthThe value of acceleration due to gravity decreases as we go below the earth surface due to decrease in the effective mass of earth. It becomes zero at the center of the earth. g' ∝ 1(R – h)2The value of acceleration due to gravity is maximum at the earth's surface and decreases with height and depth. It becomes zero at the center of the earth.MEMORY TIPS

178 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 179Consequences of variation in the value of acceleration due to gravity (g)Acceleration due to gravity is dependent upon the mass of the planet and the distance of the object from the centre of the planet. Therefore, even on the same planet, an object at different distances from the Earth, experiences different acceleration due to gravity from Earth. Since the value of ‘g’ varies from place to place, the following consequences are observed on the earth. i. Objects fall faster in the polar region than in the equator. The value of g at the polar region is greater because the radius of the earth at the poles is less. Since the value of g is higher at the poles, objects accelerate faster and reach the ground faster at the poles. Whereas, in the equator, the value of g is lesser because the radius of the earth at the equator is greater. As a result, objects accelerate slowly and reach the ground later compared to poles. Similarly, the object falls faster in the Terai region of Nepal than in the mountain region because the Terai region has more value of g due to its shorter radius. ii. The weight of the object is less at the top of the mountain than at the foot of the mountain. The top of the mountain is at a longer distance from the centre of the earth than the foot of the mountain. So, the top of a mountain has the lesser value of g, hence less weight. The bottom of the mountain has a greater value of g, hence more weight. Similarly, the weight of the load we carry becomes less when we climb mountains because of a decrease in the value of g due to an increase in height. Similarly, the weight of an object is higher at the Kechana Kawal of Jhapa than in Kathmandu because the value of g is higher at the Kechana Kawal of Jhapa due to the shorter radius. iii. A marble and a feather are dropped simultaneously in a vacuum from the same height and reach the ground together because both of them accelerate with the same value of g. Similarly, a satellite and a meteor at the same height from the Earth will accelerate with the same value of g because they are at equal height from the Earth. iv. The weight of a body is maximum on earth at the polar region. The weight of a body is more there because those places have shorter radii and greater values of acceleration due to gravity. v. Since the moon has less acceleration due to gravity, the weight of the body decreases if it is taken from Earth to the moon. vi. The weight of the object is less in the coal mines than at the surface of the earth because of a decrease in value g due to a decrease in the effective mass of the earth. Mass and WeightACTIVITY 21. Take a small stone (lighter) and a big stone (heavier) in the classroom. 2. Use weighing machine to measure their mass. Also, measure their weight with the help of a high range spring balance. 3. Lift them on your hands too. On which one stone do you apply more force in upward direction? Obviously the big stone.An object with more mass is attracted with more force towards the center of the earth. So, we need to apply more force to lift the object in upward direction against the downward force.

180 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 181MassThe total quantity of matter contained in a body is called mass. It is a scalar quantity. The SI unit of mass is 'kg'. Mass is measured by using a beam balance. The mass of a body remains the same everywhere in the universe. It means a body contains the same mass on the earth, on the moon or anywhere in the outer space. Mass of a body depends upon the size of atoms or molecules and the number of atoms or molecules.WeightThe force with which the heavenly bodies like planets, satellites etc. attract a mass towards their center is called weight. It is a vector quantity. The SI unit of weight is newton (N). It is measured with the help of a spring balance. Weight of a body is equal to the product of mass of a body 'm' and the acceleration due to gravity 'g'.i.e. Weight = mass × acceleration due to gravityor, W = m × gThe weight of a body changes from place to place. It depends upon the mass of the body (m) and acceleration due to gravity (g) at that place.FACTS WITH REASONSIt is easier to lift a small stone than the bigger one. The bigger stone has more molecules and more mass in it. Hence, they have more weight. So, we need to do more work against gravity to lift bigger stones. But the smaller stones have fewer molecules, less mass and less weight. So, we need to do less work against gravity to lift them. Therefore, it is difficult to lift a big stone on the surface of the earth and it’s easy to lift a smaller one. Variation in weight of a body due to the change in acceleration due to gravityThe weight of a body with mass 'm' is given by W = mg. The weight of a particular mass is directly proportional to the acceleration due to gravity, i.e. W ∝ g.FACTS WITH REASONSWeight of a body at the center of the earth will be zero, why?The value of acceleration due to gravity 'g' is zero at the center of the earth. Thus, weight of the body at the center of the earth W = mg = 0. So, weight of a body at the center of the earth will be zero.Variation in weight of an object when it is carried from the equator to the pole of the earthAcceleration due to gravity of the earth at pole (9.83 m/s2) is greater than that at the equator of the earth (9.78 m/s2). The greater value of acceleration due to gravity at the pole of the earth results in more weight of an object at the pole.

180 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 181FACTS WITH REASONSThe weight of a body changes from place to place on the earth. Why?The weight of a body is given by W = mg, where 'm' is the mass of the body and 'g' is the acceleration due to gravity at that place. It shows that the weight of a body is directly proportional to the acceleration due to gravity, i.e. W ∝ g. The value of 'g' changes from place to place on the earth. Therefore, the weight of a body changes from place to place on the earth.Variation in weight of an object when it is carried above and below from the earth surfaceThe acceleration due to gravity at height 'h' from the earth surface is given by : g' = GM(R + h)2 where 'M' is the mass of the earth and 'R' is its radius.i.e. g' ∝ 1(R + h)2As height from the earth surface increases, the value of acceleration due to gravity decreases. Thus, the weight of an object decreases on carrying it above the earth surface. Also, the value of acceleration due to gravity decreases at a certain depth from the earth surface. This causes decrease in weight of an object below the earth surface.Variation in weight of an object when it is carried from the earth to the moonThe average value of acceleration due to gravity on the earth surface (ge) is 9.8 m/s2 and that on the moon (gm) is 1.63 m/s2, i.e. gm = 16 ge. As a result, the weight of an object becomes almost 6 times less when it is carried from the earth to the moon. Therefore, it becomes easy to lift a heavy mass in the moon.FACTS WITH REASONSA person who can lift 50 kg in the earth can lift approximately 300 kg in the moon. why?The gravity of the moon is approximately one sixth of the earth. So, a person who can lift 50 kg in the earth can lift approximately 300 kg in the moon.Solved Numerical 7.7A man can lift 50 kg mass on the earth. How much mass can he lift on the surface of the moon. (Acceleration due to gravity on the moon is 1.63 m/s2 ).Solution: Given Mass lifted on the earth (me) = 50 kg Acceleration due to gravity on the earth (ge) = 9.8 m/s2 Mass lifted on the moon (mm) = ? Acceleration due to gravity on the moon (gm) = 1.63 m/s2The weight lifting capacity of a man remains the same on the earth and on the moon, i.e. weight lifted on the moon = weight lifted on the earthIn Nepal, weight (W) as well as acceleration due to gravity(g) is maximum in Kechana kawal (Jhapa).MEMORY TIPS

182 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 183 mm × gm = me × geor mm = me × gegm = 50 × 9.81.63 = 300.61kgThe mass that can be lifted by the man on the moon is 300.61 kg.Differences between mass and weight.Mass Weight1. The total quantity of matter contained in a body is called mass.1. The force with which the heavenly bodies like planets, satellites etc. attract a mass towards their center is called weight.2. It is a constant quantity. 2. It is a variable quantity. It changes with the change in the value of acceleration due to gravity.3. It is a scalar quantity. 3. It is a vector quantity.4. The SI unit of mass is kilogram (kg). 4. The SI unit of weight is newton (N).5. The mass of an object can never be zero.5. The weight of an object can be zero. In the condition of free fall, in interplanetary space (where g = 0), etc. the weight of an object is zero.Free FallLet’s discuss an imaginary scenario. Let’s suppose we have to land one satellite on Mars and another one on the moon. Will the parachute help to land the satellite safely on Mars as well as the moon? As far as we know Mars has an atmosphere but the moon does not. Air is fluid. It produces upthrust. If any object falls in the air, air provides resistance. The air resistance produces drag force in the falling object. The upthrust, air resistance and drag forces acting on an object slow down the falling object. If drag force from air resistance is sufficient, then the object will gain uniform velocity. Its acceleration will be zero. Then it falls with a certain uniform velocity and can land safely. Therefore, since there is air on Mars, parachutes can work. When the falling satellite uses its parachute, the parachute covers a huge area. It receives more upthrust, more air resistance and more drag force. So, it gains uniform velocity and zero acceleration. Therefore, the satellite can land safely on Mars.But what about landing a satellite on the moon? The moon is too small. It has very weak gravity. It cannot hold air to form the atmosphere. So, there is no atmosphere on the moon. When a satellite falls to the moon using a parachute, the parachute does not work. Parachute receives no upthrust, no air resistance and no drag force. The velocity of the falling satellite does not become uniform. The acceleration of the falling satellite will not be zero. The satellite will accelerate at the rate of 1.63m/s2. Hence, it will gain momentum and collide with the surface. So, satellite landing is risky on the moon. Here, scientists use thrusters and jets to gain uniform velocity and land the satellite on the moon.Acceleration produced on a freely falling body is equal to the acceleration due to gravity. For example, the acceleration of a freely falling body on the moon is 1.63 m/s2.MEMORY TIPS

182 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 183Now, let’s analyse the above situations. In the mars, the satellite landed with uniform velocity. Besides being pulled by the gravity of Mars it was affected by air resistance. Therefore, it is not a free fall.In the moon, besides being pulled by the gravity of the moon, no other forces and air resistance acted on the landing satellite. Therefore, it was in a state of freefall. But if thrusters are used to gain uniform velocity, it cannot be called freefall.Therefore, it can be concluded that the falling of an object due to gravity only, without any external resistance is called a free fall. For example, a coin dropped from a bridge, a broken falling lift, Rainfall, hailstone etc. ACTIVITY 31. Take two identical sheets of a paper. Crumple one sheet of paper into a ball.2. Drop the paper ball and the full sheet of paper at the same time. What happens?3. Now drop a TT ball and the paper ball at the same time and notice what happens.Consequences of freefall i. WeightlessnessWhen an object is in freefall, no net downward force acts on it. So, it becomes weightless even though it is inside the gravitational field of the earth. When a body is falling freely, its weight appears to be zero which is termed weightlessness due to freefall.ii. Acceleration produced on objects at freefall is independent of their mass. The acceleration of an object at freefall is equal to the acceleration due to the gravity of that planet at that place. iii. Satellites do not need any energy to revolve around the earth because they are constantly in a state of freefall. Also, the satellite is balanced by the outward centrifugal force created by velocity and the inward force created by the centripetal force due to the force of gravity. iv. An object at freefall has uniform acceleration (constant value of g). Its velocity keeps increasing uniformly at the same magnitude. For example, if g is 9.8 m/s2. Its velocity will be 9.8 m/s in the first second. Its velocity will be 9.8 +9.8 = 19.6 m/s after another one second. v. A ball dropped on a broken falling elevator does not reach the floor of the elevator because both the elevator and the ball are in freefall. There is no downward force acting on the ball as well as an elevator. So, the distance between the ball and the elevator will not decrease. Effect of air resistance on a falling object:i. Terminal velocityWhenever an object falls in a fluid (air or water) it experiences an upthrust, resistance and a drag force. Due to this, the falling object cannot get a higher velocity than a fixed Italian Physicist Galileo Galilei recognized the fact that all bodies, irrespective of their masses, are accelerated towards the earth with a constant acceleration. He did this experiment by dropping different size cannon balls from the leaning tower of Pisa in 1590 A.D. MEMORY TIPS

184 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 185velocity called terminal velocity. Therefore, the raindrops, the hail stone and skydivers fall at uniform velocities after they fall for a few durations. So, the raindrops, hail stone etc, do less damage even if they fall from a greater height. ii. Parachutists land safely using a parachute in the Earth. When a Parachutist jumps from a flying aeroplane, they accelerate for a short time. Their velocity increases for a short duration. But after the parachute opens, air exerts pressure in an upward direction against gravity. The upthrust and the drag force act on it. In this condition the rate of change in velocity of the parachute becomes uniform. The acceleration of a parachute becomes zero. Thus, the paratrooper falls slowly and lands safely on the ground. More or less same condition also appears in the dispersal of hairy seeds.iii. The parachute does not work on the moon.It is not possible to have a safe landing on the moon because the moon does not have air. The parachute will not receive upthrust and air resistance. So, its velocity will increase continuously and landing could hurt seriously. iv. No fall is freefall in the earth. No fall is freefall in the earth because any falling object experiences air resistance, upthrust and drag force within the atmosphere of the earth. v. A squeezed paper reaches the ground earlier than a flat paper when dropped from a certain height in the earth. The squeezed paper has a lesser surface area and the flat paper has more surface area. The squeezed paper receives less air resistance, less upthrust and accelerates more. The flat paper receives more air resistance, more upthrust and accelerates less. As a result, the squeezed paper reaches the ground earlier than the flat paper when dropped from a certain height in the earth. vi. A feather and a coin (guinea) fall simultaneously on the surface of the moon. The lunar surface does not have air. So, the guinea and the feather do not experience air resistance and upthrust. The acceleration due to gravity does not depend upon the mass of guinea and feather. So, objects are bound to fall at the same time and both of them reach the ground at the same time.Acceleration produced on a body during free fall is independent of its massThe acceleration produced on a freely falling body is independent of its mass. Earlier it was thought that the lighter objects fall slowly and the heavier objects fall more rapidly when dropped simultaneously from the same height. Later on, Galileo Galilei concluded that the acceleration of an object falling freely towards the earth does not depend on the mass of the object. He suggested that when a lighter feather and a heavier coin are dropped simultaneously from a certain height on the earth surface, the coin falls faster. It is due to the larger surface of the feather which experiences more air resistance and speed gets decreased. If the coin and feather would have been dropped in a vacuum then they would fall at the same rate. This experiment was performed by Robert Boyle.

184 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 185Robert Boyle's experiment (Feather and coin experiment)The British scientist Robert Boyle performed an experiment to prove Galileo's argument about the same acceleration of the freely falling bodies. He dropped a coin and a feather in a big glass jar. In this condition, the coin reached to the bottom earlier than the feather. Next time, he ejected air from the glass jar by using a vacuum pump. Now, he dropped both coin and feather together. At this time, he observed that they hit the bottom at the same time. ConclusionThe acceleration produced on the freely falling bodies is the same for all bodies and it does not depend upon the mass of the falling bodies.WeightlessnessACTIVITY 4Let’s take a steel beaker. Let’s tie a stone in the rope. Then tie another rope along the diameter of the mouth of the beaker. Tie a rope with stone to the rope used as the diameter of the mouth of the beaker as shown in diagram A. Now, if we catch the rope by the end and hang the entire set, it looks as shown in Figure A. What happens if we drop the entire set? Will it look like diagram A or diagram B? Drop the set three times, observe and conclude. Yes! When the entire set is dropped, it looks like diagram A. It does not look like diagram B. Even though we dropped the set, the set looks like as seen in diagram A because the stone and the beaker both are at freefall. Since both of them are pulled by the gravity of the earth, they accelerate equally. There is no net force pulling the stone down. Hence, the gap between the stone and the beaker does not change. Their weight becomes zero. Similarly, If the spring balance along with the apple being weighed on it are dropped together its weight will appear zero in spring balance. Here, the apple became weightless due to freefall. A BIt is our common experience that when we jump from a height we feel decrease in our weight. Momentarily, we feel decrease in our weight when the lift descends. A body has weight due to the force of gravity. When we stand on the rigid support on the earth we feel upward contact force or reaction from the support. This reaction makes us feel our weight. While jumping from a certain height we feel temporary loss of weight. It is called weightlessness. Thus, when a body is in a state of zero weight, it is called weightlessness. Weightlessness in a SatelliteWhen a satellite is revolving in an orbit, it experiences an acceleration known as centripetal acceleration. For example, the International Space Station (ISS) is a satellite where astronauts can spend days or even months in space. The astronauts and satellite have exactly the same GuineaAirA BFeatherVacuum

186 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 187acceleration towards the earth. The normal force exerted by the floor of the satellite on the body of astronauts is zero. Thus, an astronaut in a satellite feels weightless.FACTS WITH REASONSA satellite does not need any energy to revolve around the earth, why?A satellite does not need any energy to revolve around the earth because of the freefall toward the earth produced because of gravitation (centripetal force). Weightlessness in the SpaceWe know that acceleration due to gravity becomes weaker with the increase in distance because it is inversely proportional to the square of the distance. So, when an object is very far in space, the gravity of the Earth cannot reach it. Its acceleration due to gravity from the earth becomes zero. Hence, its weight will also be zero. W = m × g = m × 0 = 0 N. Such a condition is called weightlessness in the space. Differences between free fall and weightlessness.Free fall Weightlessness1. The falling of an object due to gravity only, without any external resistance is called a free fall.1. The condition in which the weight of an object becomes zero even if it has mass is called weightlessness. 2. Freefall occurs inside the gravitational field only.2. Weightlessness can occur inside as well as outside of the gravitational field. 3. It is one of the many causes of weightlessness.3. Sometimes it is caused during freefall. It occurs very far in space or at the centre of the planet too.Equations of motion for the bodies falling freely under gravityThe equations of motion for a body under uniform acceleration can be applied to the motion of a freely falling body. For this, acceleration 'a' should be replaced by 'g', Also the distance 's' is replaced by the height 'h'.Note: i. For a body thrown vertically upward, acceleration a= -g.ii. If a body is dropped down, initial velocity (u) = 0 iii. If a body is thrown up, the final velocity (v) = 0Equation for linear motions are listed below. In this case, the acceleration of an object is indirectly proportional to the mass of object and directly proportional to force as described by second law of motion.Equations of motion for an object in a straight line that works against the gravity by moving in the opposite direction of gravity. Equations of a motion for an object at freefall. In this case acceleration produced in an object is independent of mass of the object by dependent upon force of gravity of the planet.v = u + at v = u - gt v = u + gt

186 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 187s = ut + 12at2 h = ut - 12gt2 h = ut + 12gt2 v2 = u2 + 2as v2 = u2 - 2gh v2 = u2 + 2ghSolved Numerical 7.8If a coin is dropped from a 15 m tall building, how long will it take to reach the ground? Calculate the velocity of the coin when it hits the ground. Solution: Given dataHeight (h) = 15 m Time (t) =?Initial velocity (u) = 0 m/s Final velocity (v) =?Acceleration due to gravity (g) = 9.8m/s2 t = 2hg = 2 × 159.8 = 309.8 = 3.0612244 = 1.749 = 1.75 seconds Again. Final velocity (v) = u + at = 0 + 9.8 × 1.75 = 17.15 m/sHOT SKILL HIGHER ORDER THINKING SKILL1. Rachit suggests a trick for gaining profit in a business. He suggests buying oranges from the mountain and selling them to Terai at the same price using beam balance. Will there be profit? Discuss. Since he is using beam balance to buy orange in the mountains and sell them in Terai, his trick for earning more profit will go wrong.The plan will go wrong because the beam balance measures the mass of the orange. The mass of orange remains the same in the mountain region and Terai region.It appears that he has mistaken weight for mass. The orange would measure less weight in the mountain and more weight in Terai. He might have made some profit, if he had used spring balance. 2. We feel uneasy when our seat on the Ferris wheel moves downward. We feel uneasy when our seat on the Ferris wheel moves downward because the centrifugal force and gravitational force are acting in the same direction. We are at freefall at that moment. We become weightless at that moment. So, we feel scared, eerie, strange and mysterious feelings etc. at that moment. 3. The moon can cause a tide in oceans but not in Phewalake.The gravitation depends upon the mass of two interacting bodies. The mass of the ocean is more so there will be stronger gravitation between the moon and the ocean. As a result, there will be tides on the ocean. However, the water in Phewalake has a smaller mass. So, there will be lesser gravitation between Phewalake and the moon. As a result, tides are not formed in Phewalake due to the moon. 4. The mass of a boy is 50 kg on earth. How much would it be on Jupiter?The mass of a boy is 50 kg on the earth, it will be still 50 kg on Jupiter. It is because mass is constant. It does not change with changing place.

188 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 1895. An object of mass 1 kg and another object of mass 10 kg are at same height from the surface of the earth. If the object of mass 1 kg is accelerating at 1m/s2, what will be the acceleration of the object of the mass 10kg? If the acceleration due to gravity of an object of mass 1 kg in outer space is 1m/s2, then the acceleration due to gravity acting of the second object of mass 10 kg will also be 1 m/s2. Acceleration due to gravity depends upon the mass of the planet and distance from the centre of the planet. Both of them are attracted by the same planet and both of them are at equal distance from the planet. So, they must have equal acceleration due to gravity. Acceleration due to gravity does not depend upon the mass of the object. 6. If the gravitational force between two objects on Earth is 700 N, what is the gravitational force between those two objects on the moon?Gravitational force depends solely on the masses of the objects and the distance between them. So, if the gravitational force between two objects on Earth is 700 N, and you move those same objects to the Moon while keeping their masses and distance unchanged, the gravitational force between them would still be 700 N because gravitation is not affected by another medium. 7. When apple breaks from tree, we can see the falling of the apple but not the lifting of the earth, why? According to the Newton’s second law of the motion, the acceleration produced on the object is inversely proportional to its mass. So, we see the falling of the apple because the apple has very little mass, so the acceleration produced in the apple is high enough to be noticed. But we do not see the lifting of the earth because the mass of the earth is very high, so the acceleration produced on earth is not noticeable.8. What happens to the acceleration due to gravity of the earth, if it is compressed to the size of the moon. The mass of the Moon is about 1/81 times the mass of the Earth and its radius is about 3.7 times less than the radius of the Earth. Solution Case I Mass of the earth = MThe radius of the earth = RMass of the moon = M81The radius of the moon = R3.7 Case II The earth is squeezed to the size of the moon:Then the mass of the new earth = M (because mass does not change when squeezed)The radius of the new earth = radius of the moon = R3.7 Now, Acceleration due to gravity of new earth (g’) = R3.72GM = 13.69, GMR2 = 13.69 gTherefore, if the earth is compressed to the size of the moon its acceleration due to gravity will be 13.69 times more than its current acceleration due to gravity.

188 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 1899. What will be the acceleration of a freely falling object on earth and that falling with a parachute? Why?The acceleration of a freely falling object will be exactly 9.8 m/s2. It is because a freely falling object is not affected by external forces except gravity from the earth. The acceleration of an object falling with a parachute will be 0 m/s2. It is because the air resistance acting on the parachute stops acceleration. An object falls with uniform velocity. So, an object will have zero acceleration. 4 STEPS EXERCISE EXERCISESTEP11. Multiple Choice Questions a. In which direction does the force of gravity act? i. east of the planet ii. west of the planet iii. toward the centre of the planet iv. north-east of the planet b. Where is the value of g maximum?i. inside the earth ii. at the centre of the earth iii. at the surface of the earth iv. above the earth c. What is the force produced because of the masses of the objects?i. pressure ii. density iii. gravitation iv. electrostatic force d. Let the value of g on the surface of the earth be gs, on the coal mine be gm and at the top of Mount Everest is gh. Which of the following order is true?i. gm > gs > gh ii. gm > gs < ghiii. gh < gm < gs iv. gm < gs > ghe. If the mass of the earth is halved and the radius is doubled, what will be its acceleration due to gravity?i. 18 g ii. 14 g iii. 12 g iv. 4 g f. Select the best option after studying the given statement and arguments. Statement: When we drop a marble and a feather from the table, the marble reaches the ground earlier. Argument 1: Of course! The marble is heavy it falls faster than the feather.Argument 2: The marble and the feather fall together because the acceleration produced on them does not depend upon their mass in the earth.i. Statement is correct. Both arguments are wrong. ii. Statement is incorrect. Both arguments are correct. iii. Statement and argument 1 are correct. Argument 2 is incorrect. iv. Argument 1 and argument 2 are correct. The statement is wrong. g. When an object is brought from the earth to the height of 36,000 km, how can a decrease in its weight be described?

190 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 191Distance between them Acceleration due to gravity Mass of the object i Increases Increase Constant ii Decreases Decreases Decreases iii Increases Increases Increases iv Increases Decreases Constant h. What are the consequences of the gravitation?i. formation of the solar system, formation of a star, production of solar energy ii. formation of galaxies, expansion of the universe, big bang explosion iii. determination of the shape of the universe, the atmosphere around the earth, alignment of planets in the solar system iv. formation of galaxies, falling of an apple, weak nuclear force i. Find the weight of the body shown in the given figure. i. 24.5 N ii. 19.6 N iii. 2.45 N iv. 196 N j. Write the relation between gravitation and the product of masses. i. F ∝ m1m2 ii. F ∝ 1d2iii. F ∝ 1m2 iv. g ∝ m1m2a. iii b. iii c. iii d. iv e. i f. i g. iv h. iii i. i j. i Ans of MCQSTEP22. Very short questions a. Which planet has the highest gravity among A, B, C and D? More mass Less mass Longer radius A BShorter radius C D b. What is the nature of gravitational force?c. In which case among A, B and C, the weight of the object is highest if mass of the earth is constant. R + h AR BR – h Cacceleration due to gravityd. If the gravitational force acting on a 75-kilogram object 6400 kilometres away from the centre of the earth is 735 N, what would be the weight of an object?h = 6400 km10 kgR= 6400 kmEarth

190 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 191e. What is the value of G in Jupiter? f. A person can lift 100 kg mass on the surface of the earth. How much mass can he lift on the moon's surface? g. The moon is very small compared to the sun, but it exerts greater gravitational pull in the ocean and creates tides. Why?h. Write the main conclusion of Galileo’s feather and coin experiment i. Satellites do not need any energy to revolve around the earth, why?STEP33. Short questions a. Parachute was used to safely land the Perseverance rover on Mars. What was the role of the parachute there? b. To estimate the height of the Koshi Bridge over the river, a stone is dropped freely into the river from the bridge. The stone takes 2 seconds to touch the water surface. Calculate the height of the Koshi Bridge from the water level. c. Differentiate between g and G where the letters have the usual meaning. d. Why is the value of 'g' more in Terai than in the mountain?e. Stones of 1 kg and 5 kg masses are dropped from the same height on the moon's surface, which one will reach the surface faster and why? f. How much is the weight of a 1 kg mass at the pole and the equator of the earth? Calculate. g. Acceleration due to gravity is calculated by the equation g = GMR2 . If the object is placed at the top of Mount Sagarmatha, the value of g decreases. How will this situation affect the value of the gravitational constant (G) in the given equation?h. The moon can cause a tide in oceans but not in Phewa taal. Give reason. STEP44. Long questions a. In the given figure an apple is falling towards the earth's surface. Based on the given figure answer the following questions.i. Why does an apple fall toward the ground?ii. If an apple and a leaf of apple are dropped simultaneously, which one reaches the ground first and why?iii. What is the change in velocity in the apple and leaf of the apple in every one second if there is no air resistance?b. The earth revolves around the sun as shown in the given figure. What happens to the magnitude of the gravitational force of the sun when the earth is at point A and point B? Why does the earth revolve around the sun SunAB

192 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 193as in the given figure? The earth revolves around the sun but does not fall to the sun. Why? c. Observe the given figure and answer the following questions.i) What is the given experiment called?ii) Who performed it for the first time?iii) Write the objective and conclusion of this experiment.d. Study the given paragraph and answer the following questions. [Everything that has mass also has gravity. An object with greater mass can produce greater gravity. Gravity gets weaker with distance. The entire mass of the earth pulls all the mass present in our bodies. As a result, we have weight. Gravity holds the moon in its orbit around the earth and the moon brings tides in the ocean. Gravity holds down the atmosphere and holds our world together. Gravity isn’t the same everywhere. It is weaker inside the coal mines, on top of Mount Sagarmatha and in equatorial regions.]The radius of the earth up to sea level is 6371 km and the height of Mt. Sagarmatha is 8848 m. If a person of mass 80 kg goes from sea level to the top of Mt. Sagarmatha, what happens to the weight of that person? Why does it happen? How much change in the weight of that person can be observed? Show by calculation. 5. Numericali. Observe the given figure and find the gravitational force between m1 and m2. [Ans: 4 × 10-10 N]2mm1 = 6 kg m1 = 4 kgii. The mass of the earth is 6 × 1024 kg and that of the moon is 7.4 × 1022 kg. If the average distance between the earth and the moon is 3.84 × 105 km, calculate the force exerted by the earth on the moon (G= 6.67 × 10-11 Nm2 kg-2).[Ans: 2.01 × 1020 N]iii. Let’s suppose there are two planets around a star in the star system. Today they are aligned in a straight line. Let the mass of the star be 4M, the mass of the first planet at a distance ‘d’ from the sun be 2M and the mass of the second planet at a distance 3d from the sun is M. Let’s suppose the gravitation between the star and the first planet is F. Then calculate the gravitational force between first planet and second planet in terms of F. [Ans: F/16]3dd4M2M M

192 F oRce and Motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 193iv. The mass of the earth is 6 × 1024 kg and its radius is 6.4 × 106 m. An apple of 200g falls on the earth's surface. Find, (i) the acceleration produced on the apple by the earth. [Ans: 9.77 m/s2](ii) the acceleration produced on the earth by the apple. [Ans: 3.26 × 10-25 m/s2]v. The gravitational force between the two masses at a distance of 2.5 × 104 km is 250 N. What should be the distance between them to reduce the gravitational force by half? [Ans: 3.536 × 107m]vi. Ramesh and Shyam are playing with water balloons. Ramesh is on the roof and Shyam is vertically below the roof. They throw balloons to hit each other at the same time. Ramesh threw the balloon downward at a velocity of 10 m/s and Shyam threw the balloon upward at a velocity of 15 m/s. Both balloons are moving in a straight line. The balloon collided mid-air after 1.5 seconds. What distance balloon thrown by Ramesh covered? What distance balloon thrown by Shyam covered? Calculate the height of the building. [Ans: Balloon thrown by Ramesh covered 26.025 meters, balloon thrown by Shyam covered 11.475 meters, height of the building is 37.5 meters]vii. If the earth is compressed in such a way that its volume becomes equal to that of the moon, the mass of the earth is 6 × 1024 kg and the radius of the moon is 1.7×106m. Find the acceleration due to gravity on the new earth. What will be the weight of a 100 kg mass on that earth? [Ans: 138.48 m/s2 13,848 N]viii. Let’s suppose Elon Musk kept two satellites in low earth orbit at the same distance from the surface of the earth. Let the mass of the first satellite is m1 and the mass of the second satellite is m2. Elon Musk found that the gravitational force between the Earth and the first satellite is equal to the gravitational force between the Earth and the second satellite. Then he stated that both satellites must have equal mass. ie. Mass of first satellite (m1) = mass of second satellite (m2). Is his statement correct? Verify with calculations. ♦♦♦

194 PRessuRe Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 195Key terms and terminologies of the unit1. Pressure: The force acting perpendicularly per unit area is called pressure.2. 1 pascal pressure: The pressure exerted by 1N force acting normally upon the area of 1m2 is called 1 pascal pressure.3. Liquid pressure: The thrust exerted by a liquid per unit area of the surface in its contact is called liquid pressure.4. Pascal's law: Pascal's law states that \"liquid transmits pressure equally and perpendicularly in all directions when pressure is applied at a point on a liquid kept in a closed container\".5. Hydraulic machines: Hydraulic machines are the devices which multiply force on the basis of Pascal's law. 6. Upthrust: The resultant upward force acting on an object when partially or wholly immersed in a liquid is called upthrust. 7. Archimedes' principle: Archimedes' principle states, 'when a body is wholly or partially immersed in a liquid, it experiences an upthrust which is equal to the weight of the liquid displaced by it.'8. Law of floatation: According to law of floatation, 'a floating body displaces liquid equal to its weight. IntroductionWe use a sharp knife to cut vegetables and a sharp axe to chop the wood. It is difficult to insert a blunt nail into the wood. Similarly, a camel can walk easily in a desert but a horse cannot. These discussions prove that pressure depends upon two factors, viz. force and area. Thus, the force acting perpendicularly per unit area is called pressure. From the definition,Sequence of Curriculum Issued by CDC Introduction to pascals law and its application in daily life activities  Introduction toupthrust Introduction and application of Archimedes' principle UNITPressure8Estimated teaching periods Theory Practical4 1Suresh Bhattarai, a distinguished physicist from Nepal, has made substantial contributions to the fields of astronomy and space science. Serving as a lecturer at Tri-Chandra Multiple Campus and Chairperson of the Nepal Astronomical Society, Bhattarai is deeply committed to education and outreach efforts in these disciplines. His dedication and achievements have garnered prestigious awards such as the SGAC Young Leadership Award and NAST Science and Technology Promotion Award. Suresh BhattaraiAbout the Nepalese Scientist

194 PRessuRe Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 195Pressure (P) = Force (F)Area (A)This formula shows that pressure is directly proportional to the force applied and inversely proportional to the contact area. Pressure is a scalar quantity. The SI unit of pressure is N m-2or pascal (Pa). To increase pressure we should increase the force applied and decrease area. FACTS WITH REASONSA camel walks easily on sand, but it is difficult for a horse to walk on the sand though the camel is much heavier than the horse, why?The hooves of camel have large area. The weight of camel spreads on a large area of sand. Due to this, the pressure created on the sand becomes less and camel's feet do not dig in more. On the contrary, the feet of a horse have a small area. The body weight of the horse is distributed over a small area of the sand. This results in more pressure on the sand and it becomes difficult for a horse to walk on the sand.Differences between thrust and pressure.Thrust (force) Pressure1. Thrust is a push or pull acting on a body.1. Pressure is the thrust per unit area of the surface in contact.2. It is independent of the area over which the force is applied.2. It depends upon the area on which the force is applied.3. It is measured in newton (N). 3. It is measured in pascal (Pa).4. It is a vector quantity. 4. It is a scalar quantity.FACTS WITH REASONSPressure is a scalar quantity, why?Pressure is a scalar quantity, though it is the perpendicular force per unit area. In case of liquid, the pressure is exerted equally in all directions, which means that pressure has no definite direction. Transmission of pressureThe solids cannot transfer pressure through them because their molecules do not change place. Solids exert pressure where they come in contact. Liquid molecules can move. So, they can transfer pressure. They can transfer pressure equally in all directions because liquid molecules are incompressible. Their intermolecular distance is fixed. Gas molecules can move. So, gas molecules can also transfer pressure. Gas molecules are compressible. Their intermolecular distance is not fixed. If we apply sufficient pressure, gas molecules stay closer. Their volume can decrease. So, they cannot pass pressure equally. They transfer pressure through them partially. The gas kept in a closed container at a high pressure is called compressed air. The compressed air has a fixed intermolecular distance. It cannot be further compressed. Therefore, compressed air can transfer pressure equally in all directions. Transferred pressure can multiply force and do work at another place. Liquids have very little space between their molecules. So they don't change shape when they're pushed from the outside. This means liquid can't be compressed.MEMORY TIPS

196 PRessuRe Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 197Liquid PressureLiquid does not have its own shape. When a liquid is poured into a container, it applies pressure on the sides and at the bottom of the container. Liquid applies thrust on the walls of the container which causes pressure on the container. The thrust exerted by a liquid per unit area of the surface in its contact is called liquid pressure. Liquid also exerts pressure on any object in the liquid. ACTIVITY 1a) Take a glass tube which is open at both ends and fix a balloon to one end of the glass tube.b) Hold the tube and fill the tube with water. Do you observe an increase in size of the balloon with increase in height of water column in the glass tube?Water exerts pressure which makes the balloon expand. Such pressure increases with increase in column of the water and the size of balloon also increases.Properties of Liquid Pressurei) Liquid applies pressure in all directionsLiquids have a weak force of attraction among their molecules. They push the walls of the container or surfaces in contact. If a liquid is kept in a container and pressure is applied from any point, the applied pressure transmits equally in all directions.ii) Pressure increases with depth At a point in greater depth, the weight of liquid above the point increases. This causes high pressure.FACTS WITH REASONSIn domestic water supply, the pressure on the ground floor is higher than the water pressure upstairs, why?Water tanks are kept on the roof of a building. The downstairs taps have more depth of liquid column from the tank. Since liquid pressure increases with depth, in domestic water supply, the pressure on the ground floor is higher than the upstairs.iii) Pressure does not depend upon the shape of the containerWhatever the shape or width, the liquid pressure at a particular depth is the same.iv) Pressure depends on the density of the liquidThe liquid with more density applies more pressure at a particular depth than the liquid with less density.There are a lot of empty spaces between the molecules of a gas. So, they can easily change shape when pressure is applied on them from the outside. As a result gas can be compressed.MEMORY TIPSLiquid pressureLiquid in different shape container