Modern Concept Science and Technology 10 New

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 147 B. Human induced causes of climate change Some 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 earth The 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 Chlorofluorocarbons (CFCs) emitted by coolants and aerosols reach the upper stratosphere and break down ozone gas. This lets more UV rays enter the earth increasing temperature of the earth. This causes change of climate over a long time. Use of CFCs in refrigerators, AC should be replaced by ammonia. Why? Refrigerators, ACs, deodorants, etc. with CFCs are bad for ozone layer as they release gases called Chlorofluorocarbons which deplete the ozone layer. But some of them contain ammonia and hydrofluorocarbons which do not deplete the ozone layer but contribute to greenhouse effect. FACTS WITH REASONS 4. 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 Any waste and its treatment produces a lot of methane gas. Methane gas is a greenhouse gas. Hence it causes global warming. 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. Deforestation Forest maintains the amount of carbon dioxide and oxygen in the atmosphere. The amount of carbon dioxide gas in atmosphere increases due to deforestation. It results in increase in temperature and 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 REASONS

148 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Effects of Climate Change i. Climate change increases the rate of snow and ice melting due to which sea levels rise. ii. Climate change can change rainfall patterns and ultimately affects plantation and harvesting of crops. iii. Climate change can result in extreme global warming. iv. It can push several organisms towards extinction. v. It can cause the natural disasters like hurricanes, GLOF, floods, avalanches, tornadoes, cyclones to occur frequently and violently. vi. It results in the flooding of coastal areas and countries like the Maldives, India (Mumbai), Japan, New York. vii. It affects the global weather pattern. viii. It causes displacement of human population near from the coastal areas. ix. It can lead to drought, famine and natural calamities due to which instability of governments might occur. x. It affects natural and cultural heritages. xi. Climate change can cause various epidemic and fatal diseases in human. Measures of climate change control and management i. Alternative sources of energy should be promoted due to which carbon emissions can be cut off. ii. Afforestation should be done in every possible barren land. Forests absorb large amount of carbon dioxide from the environment and controls global warming. iii. The solid wastes should be reduced, reused and recycled. Burning of wastes should be the last option. iv. The use of fossil fuels like petrol, kerosene, diesel etc. should be discouraged. v. Chemical fertilizers should be replaced by organic fertilizers. vi. The ozone layer depleting gases like CFCs should be completely banned. vii. Filters and high tech chimneys should be used in factories to prevent the toxic gases to escape in upper atmosphere. viii. Public awareness programmes should be conducted extensively. People should be encouraged to conserve energy sources and use public transportation for travelling as far as possible. ix. Energy efficient buildings should be constructed. x. CFCs in the refrigerators should be banned completely. xi. Development works should be conducted for necessity, not for luxury as far as possible. 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 In Nepal, environment conservation act was implemented in 2076 BS. MEMORY TIPS

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 149 are not conserved in time, they may go extinct. Nepal has many species of endangered plants and animals. Causes to extinct plants and animals i. Animals and plants go extinct mostly due to climate change and environment pollution. ii. Due to uncontrolled and excessive use of animals and plants they get extinct. iii. The development of new species of animals and plants replace old and traditional species of animals and plants. iv. Hunting and smuggling of the animals reduces its number and finally extinct. Some protected mammals are: Pygmy Hog, Red Panda, Black Buck, Gaur Bison, Wild Yak, Wild Water Buffalo, Grey Wolf, Hispid Har, 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. Some of them mammals, birds and reptiles are briefly discussed below: a) One Horned Rhinoceros Scientific name:Rhinoceros unicornis Physical characteristics: One-horned rhino is one of the protected animals of Nepal. It has rough, thick and folded skin on its body. It is blackish grey in colour. The average length of a mature rhino is about 3m to 3.8m and height extends from 1.7 to 2m. It weighs about 1800 to 2700 kg. It has one horn that grows as an extension of its nasal bone. The horn is 20cm to 61cm long and regrows if broken off. The body is hairless except around the tip of tail, ears and eyelashes. It gives birth to a single baby at a time. Food: The staple food of rhino is grass, fruits, leaves, branches of trees, shrubs and submerged and floating aquatic plants. Habitat: One-horned rhino is found in the foothills of Himalaya in the Terai region of our country. Grasslands, swamps, forest and riversides that are rich in its fodder are its habitat. Lifespan: It has an estimated life span of about 40-50 years. b) Bengal Tiger Scientific name: Panthera tigris Physical characteristics: The Bengal tiger is known best for its yellow/light orange and black/dark brown stripes. It has white underbelly and white tail with black rings on it. White spots can be seen on the back of their One horned rhinoceros Bengal Tiger

150 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur ears. Male tigers are generally larger than the female ones. A male tiger is about 3m long while a female is just about 2.75m in length. Bengal tigers have a tail of about 0.6 m to 0.9m in length. Their body weight ranges from 130 kg (Females) to 230 kg (Males). Food: Large mammals like deer, wild-buffalo, Nilgai etc. are its food. It also preys on birds and reptiles. Habitat: They live in dense grasslands and Terai forests of Nepal. They prefer habitats in which they can mimic the surrounding. Life span: Its life span is estimated about 15 years in wild. It can survive up to 20 years in captivity. c) Asiatic Elephant Scientific name: Elephus maximus Physical characteristics: An Asian elephant is one of the largest land animals. It is blackish grey in colour. It is about 2.5m to 3.5m in height. It weighs about 2250 kg to 5500 kg. It has a huge head and a long muscular trunk. It has large floppy ears, wide thick legs and a small short tail. Its incisor teeth are modified outward into long tusks. Food: Grasses, roots, fruits, fodder and bark of trees are its major sources of food. They use their tusks to pull the bark off and dig the roots of tress out of the ground. Habitat: It lives in hot and humid habitat. It is found in the forest and large grasslands of Terai region of our country. Lifespan: Its lifespan in wild is about 50-60 years. But, it can live upto 70 years in captivity. d) Red Panda Scientific name: Ailurus fulgens Physical characteristics: Red panda is a small sized mammal with long fluffy tail and red-white marking on its body. Its body is covered with reddish brown furs with white patches around the inner ears, eyes and nose. It is about 51cm to 66cm in length excluding the tail. The tail is about 25.4cm to 51cm long. It has a rounded head, large pointed ears and a stumpy muzzle. The ears are dark red on the outer surface. Food : It is a herbivorous animal but more similar to carnivorous and omnivorous bears in body structure and systems. Bamboo shoot is its major food. It also eats forage of roots, fruits and grasses. Asiatic Elephant Red Panda

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 151 Habitat: It is found in the temperate forest at an altitude of 3000m to 3500m in higher hills and lesser mountains of Nepal. It is mostly found in Rasuwa, Panchthar, Taplejung and other districts of Nepal. Lifespan: Its lifespan is about 8-10 years in wild and 15 years in captivity. Why is red panda a rare mammal? Red panda is a rare animal because its number is too few on the earth. It is found only in high altitudes and is going to be extinct. FACTS WITH REASONS e) Asiatic Rock Python Scientific name: Python molurus Physical characteristics: It is a large non-poisonous snake. It has long body, thin and slender head and tail while the middle portion of the body is thick and swollen. Its body is light brown to yellowish in colour with brown spots all over the body. Brown spots have black or dark brown boundary. It’s about 7m to 10m in length and weighs about 85 kg to 90 kg. Food: It preys on mammals like small lambs of sheep, goat, etc. It also preys on deer, rabbit, rat, squirrel, birds and reptiles. Habitat: It is found in dense forest of Terai region that is rich in dried leaves and dead logs. Moist and swampy places, grasslands and riverside bushes are also its habitat. Lifespan: Its average lifespan is about 18-20 years. f) Giant Pied Hornbill Scientific name: Buceros bicornis Physical characteristics: It has a very long bill capped with a yellow rectangular and flattened casqued. It extends over the head like hat. It is fairly large with length ranging from 95cm to 120 cm. Its wingspan is about 151cm to 178cm. It weighs about 3kg to 3.5 kg. Its body, head and wings are black. While its abdomen and neck is white. Food: It is a frugivore and feeds on lipid rich and sugar rich fruits. But, it also eats small mammals, birds, reptiles, and insects as well. Habitat: It is arboreal and lives mainly in wet, tall and evergreen forest. It prefers to live in the canopy of taller trees. It is found in Terai and Siwalik Hills of Nepal. Lifespan: Its average lifespan is about 6 to 7 years. ACTIVITY 1 Visit 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. Asiatic Rock Python Giant Pied Hornbill

152 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Conservation of endangered species of animals and birds The hunting and smuggling of the animals are making them listed in the endangered animal lists. Some of them are killed for their skin, some for their trunk, some for their bones which are of the very high cost. If these animals are completely disappearing from the earth, then there will be a huge effect on the ecosystem. The loss of habitats due to the change of ecosystem and Negative effect on the natural environment are also the factors affecting the lives of animals or birds for that matter. 1. Conservation of ecosystem The animals or birds can survive in their natural habitat. The habitats for birds and animals are provided by the natural ecosystem. If we want to conserve the rare and endangered birds and animals, we must conserve the ecosystem first. We must conserve the forest, water resources, etc. which help to conserve the ecosystem. 2. Restriction in hunting People hunt for their satisfaction and some for illegal trade. Every valuable part of those animals is taken by the hunters for illegal trade. Such activities decrease the number of birds and animals. So hunting should be strictly prohibited and strict legal actions should be taken against the offender. 3. Awareness programs At the national and local level, the awareness program should be conducted. Because the awareness program can help to give knowledge about the importance of birds, animals, and other living beings. So that the endangered animals are safe. 4. Public Participation in the conservation program If we want to conserve the endangered animals than the conservation program should be conducted. But the conservation program will only be effective if there is the participation of local people. The local people should be made responsible for the conservation of birds and animals around them. 5. Reduction of effects of human activities Well, every nation needs development but that does not mean doing unnecessary things in name of development. Well, every development activity like the construction of road, industry, building, dam, etc. bring changes in the environment. The development activities produce waste products. Sewage and harmful chemical etc. Those things can hugely affect the environment and that deplete the rare birds, animals, and other living beings too. That’s why the adverse should be controlled in the time of conducting development activities. 6. Appropriate laws and strict implementation At the national and local level, we should formulate appropriate laws and implement them strictly to conserve endangered animals and plants. 7. Ex situ conservation Some endangered animals and bird can be conserved in ex situ ecosystem like aquarium, botanical garden, zoo, zoological park, etc.

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 153 Some traditionally used medicinal plants Introduction to Medicinal plants Medicinal plants have been discovered and used in traditional medicine practices since prehistoric times. Plants produce hundreds of chemical compounds for functions including defense against insects, fungal diseases. Medicinal plants can be defined as the plants that possess therapeutic properties or exert beneficial pharmacological effect on the human or animal body. Out of 7000 flowering plants present in Nepal, more than 700 plants are used in medicines. Most medicinal plants are found in Karnali region. Examples are Tulsi, Aloevera, Flagroot, Neem, Yarshagumba etc. Some of them are discussed below: Holy basil (Ocimum tenuiflorum) It is also known as tulsi or tulasi. It is an aromatic perennial plant. It is cultivated for religious and traditional medicine purposes and also for its essential oil. It is widely used as a herbal tea, commonly used in Ayurveda. It is one of the best plants for purifying indoor air quality as it absorbs many toxic chemicals. Tulsi leaves are used to treat skin problems like acne, blackheads and premature ageing. Tulsi is used to treat insect bites. Tulsi is also used to treat heart disease and fever. Tulsi is also used to treat respiratory problems. Aloevera (Aloe vera) It is a succulent plant species which is widely distributed and is considered invasive species in many world regions. It is originated from Arabian Peninsula but grows wild in tropical, semi-tropical and arid climates around the world. It is used as a topical treatment and also as a decorative purpose. Aloe gel is used to make topical medication for skin conditions such as burns, wounds, rashes, cold sores or dry skin. Flagroot or Bojho (Acorus calamus) It is known as bojho in Nepali language. It is a tall wetland monocot as well as herbaceous perennial whose leaves resembles those of iris family. It is found in edges of small lakes, ponds and rivers, marshes, swamps and other wetlands. It has been used medicinally for gastrointestinal diseases and treating pain and its aroma makes calamus essential oil used in perfume industry. Holy basil Aloevera Flagroot

154 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Asiatic pennywort (Centela asiatic) It is a herbaceous perennial plant used as a culinary vegetables and medicinal herbs. It is known as Ghodtapre in Nepali language. The flower are white or crimson in colour. It is aquatic plant and can be cultivated in drier soils as long as they are watered regularly enough. It has been used to treat various disorders and minor wounds. It may have adverse effects on liver function when used for a long period of time. Mugwort (Artemisia vulgaris) It is known as Titepati in Nepali language. It has been used medicinally and as a culinary herb. It is very common plant growing on nitrogenous soils, other weedy and uncultivated areas. It has been used as one of the flavoring and bittering agent, fermented grain beverage. It is used as an offering to the Gods, for cleansing the environment, as incense and also as a medicinal plant. Heart-leaved moonseed (Tinospora cordifoli) It is commonly known as Gurjo. It has been used in Ayurveda to treat various disorders. It gets it name by its heart shaped leaves and its reddish fruit. Flowers are unisexual, small and appearing when the plant is leaflets, greenish yellow on axillary and terminal racemes. It has an importance in traditional ayurvedic medicines used for ages in the treatment of fever, jaundice, chronic diarrhoea, cancer, bone fracture, pain, skin disease, snake bite etc. Malabar Nut (Justicia adhatoda) It is a small evergreen, sub-herbaceous bush which grows commonly in open plains especially in lower Himalayas. Leaves are 10-16 cm in length. It requires very little watering and is an extremely hardy plant. It is called Asuro in Nepali language. It is useful for curing coughs, colds and asthma and is easy to administer. It is also used to loosen chest congestion, open the bronchi and heart spasms. Asiatic pennywort Mugwort Heart-leaved moonseed Malabar Nut

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 155 Neem (Azadirachta indica) It is a natural herb that comes from the neem tree. Its fruits and seeds are the source of neem oil. It is a fast growing tree. It is deciduous, shedding many of its leaves during dry winter months. Its leaves are dried and placed in cupboard to prevent insect eating clothes and also in tins where rice is stored. The leaf extract is used to reduce tooth plaque and to treat lice. It helps to reduce blood sugar levels, heal ulcers in digestive tract, prevent pregnancy, kill bacteria and prevent plaque from forming in the mouth. Yarsagumba or Chinese caterpillar fungus(Cordyceps sinensis) It is found in the high altitudes, basically in the Himalayan region. It is considered as a biological gold because of its high demand. It is a kind of fungi that grows out of the head of the dead caterpillar. It is an entomopathogenic fungus that acts as a parasite of insects that kills and grows on them. It is used to increase energy and decrease fatigue. It is used to treat heart diseases, mental diseases etc. Turmeric (Curcuma loga) It is found in most of the region of Nepal. Its modified stem remains in the soil. It has curcumin chemical to make it yellow and medicinally useful. It has vitamins A, B, B2, C, etc. It has different minerals like iron, calcium, phosphorus, etc. It has antimicrobial property which makes food attractive, kills microbes and increase our immunity power. It is used to eradicate leprosy, lung disease, heart disease, skin disease, etc. It is also used to colour different food items and make cosmetic products. Conservation of endangered species of plants Excessive use of some plants and their species make them in the list of endangered category. So, to conserve them we can apply following conservation methods. 1. Conservation of natural habitat The natural habitat of plants should be conserved protecting from forest fire, overgrazing, urbanization, industrialization, construction of roads, etc. 2. Increase plantation of endangered species of plants The seeds of endangered species of plants should be collected, preserved and grown in the nursery. Then, they are planted in suitable habitat to increase their number. If seeds are not available, the tissue culture method can be applied to increase their number. 3. Awareness programs towards endangered, rare and medicinal plants. At the national and local level, the awareness program should be conducted. Because the awareness program can help to give knowledge about the importance of rare, endangered and medicinal plants. Yarsagumba Turmeric Neem

156 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur 4. Appropriate laws and strict implementation At the national and local level, we should formulate appropriate laws and implement them strictly to conserve endangered, rare and medicinal plants. 5. Protection of plants from their extinction The endangered species of plants should be protected from being extinct completely. If they are very rare, we should use in situ and ex situ conservation method to protect them. HOT SKILL HIGHER ORDER THINKING SKILL 1. 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. 2. 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. State the cause of irregular rainfall on earth nowadays. The cause of irregular rainfall in various places on the earth are deforestation, forest fire, over greenhouse effect, global warming and climate change. 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 whose population has drastically declined and is about to go extinct are called endangered plants. 1 The plants whose vegetative parts, flowers, seeds, fruits or oil is used as medicine is called medicinal plants. 2 Endangered plants cannot be harvested. 2 Medicinal plants are farmed and harvested. 5. Climate change accelerates the extinction of endangered species. Climate change is bad for the environment and any organism living in it. Climate change forces endangered species to go extinct in many ways: i. Local plants cannot grow well due to irregular rainfall and an increase in temperature. It disturbs the flowering and fruiting of plants. So, the ecosystem will be disturbed due to a lack of food. ii. Organisms will be sick, smaller and cannot reproduce successfully due to change in climate. iii. Some endangered species migrate to search for suitable shelter and feeding grounds. They cannot thrive in new places either.

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 157 iv. Germs, invasive plants and animals spread from one region to another due to climate change. It can spread epidemics and kill endangered species. 6. 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? Despite the availability of medicinal herbs in our surroundings, we are still dependent upon imported medicines. The causes are: i. We do not have sufficient technology to process raw medicinal herbs into medicine. ii. Chemical medicines are easily available and cheaper than herbal medicines. We can do the following activities to increase the use of medicinal herbs. i. Encourage the use of medicinal herbs over modern medicines. ii. Train local people to collect, farm, harvest and process the medicinal herbs to make medicines. iii. Educate people about the side effects of modern medicine and the good effects of medicinal herbs. 7. 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 invites an energy crisis. Climate change invites an energy crisis indirectly. Some examples are: i. Climate change has brought drought in many places. Vegetation is lost. So, there will scarcity of biomass energy. ii. Mountain snow melts faster and finishes early due to climate change. As a result, the river will be smaller in other seasons. Hydroelectricity production will decrease. iii. If the average temperature of the earth increases, more people will use electricity to run the air conditioner, fridges and fans. iv. Stronger winds will damage wind farms. 10. Describe any two causes of climate change due to human activities. The two causes of climate change are: i. Excessive carbon emission The emission of a large amount of CO2 from the burning of fossil fuels, coal, wood, respiration, etc. contributes to the greenhouse effect due to which the overall temperature of the earth is increasing. Global warming is causing a change in rainfall, snowfall, seasonal patterns, etc. As a result, it causes climate change. ii. Industrial gases Industrial gases like the oxides of nitrogen and sulphur can significantly alter climate due to their ability to reflect or absorb solar radiation. These suspended particles can cool the air by reflecting and absorbing solar rays. Thus, over a long period, industrial gases can cause climate change.

158 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur 3 STEPS 3 STEPS EXERCISE EXERCISE STEP1 1. Choose the best answer from the given alternatives. a. What can greenhouse gases 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 iii. absorb heat from the atmosphere and decrease its temperature iv. maintain air pressure b. Which animal is called Elephus maximus? i. mammoth ii. python iii. elephant iv. rhinoceros c. What is asuro used for? i. curing cough, cold and asthma ii. curing heart attack and cancer iii. treat gastrointestinal diseases iv. to make perfume d. What is a yarsagumba? i. plant ii. caterpillar iii. fungi iv. monera e. Which plant is shown in the diagram? i. neem ii. gurjo iii. ghodtapre iv. beshar f. In which group does gurjo belong to? i. endangered ii. medicinal iii. creepers iv. thorny 2. Define the following terms with required examples. a. Climate b. Climate change c. Ozone layer depletion d. Rare species e. Medicinal plants f. greenhouse effect 3. Answer the following questions in very short. a. Write the full form of CFC. b. Which industrial gas is the main culprit for climate change? c. Where do one-horned rhinoceros usually live in Nepal? d. How much does an adult Bengal tiger weigh? e. How long does an Asiatic elephant usually live? f. What is the major food of red pandas? g. Write a use of Ocimumtenui florum. h. Write the scientific name of the mugwort and Bengal tiger. i. Which part of bhojo is used as medicine? j. What is the relation between caterpillar and fungus that makes yarsagumba? k. Experts say the sea level is rising. What is the cause?

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 159 l. What chemical of neem treats small pox? m. Which medicinal plant is good for the following? i. cough and cold ii. cancer iii. small pox iv. increase the immunity system STEP2 4. Give reasons. a. Climate change is also a cause of the extinction of species. b. Asiatic rock python is an endangered animal. c. Volcanic activities can cause climate change. d. Increase in the concentration of carbon dioxide in the atmosphere must be stopped. e. Use of fossil fuel must be reduced. f. Nepal is rich in biodiversity. g. Nepal has banned hunting of the Bengal tiger. h. Rich biodiversity of Nepal is declining day by day. i. With the increase in the use of fossil fuels, there is irregular rainfall in Nepal. j. Endangered species must be conserved. k. Tulsi water is good for health. l. Yarsagumba is used to make energy drinks. 5. Differentiate between the following. a. Extinct species and endangered species b. Holy basil and neem c. Climate change and weather d. Tulsi and gurjo 6. Answer the following questions in short. a. How does industrialization cause climate change? b. Volcanoes, wildfires and leaching can cause climate change. Discuss. c. What is Asiatic pennywort used for? d. Write a short note on a red panda. e. How does ozone layer depletion cause climate change? f. Public participation is very important for the conservation of endangered species. Discuss. g. What are endangered species? Give some examples of endangered species found in Nepal. 7. Answer the following questions based on the given figure. i. Write the scientific name of the organism shown in the diagram. ii. Write its habitat. iii. What is its average length? iv. What does it feed upon?

160 natuRe and enviRonment Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur STEP3 8. Answer the following questions. a. Discuss the harmful effects of climate change on human beings. b. What kind of changes in the environment are observed due to climate change? c. 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? d. 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. 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. f. 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. g. How will the extinction of species hurt human beings? What can be done to prevent rare species from going extinct? h. 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. i. Even though elephants raid villages and crops and sometimes kills people, it is still illegal to hunt down wild elephants in Nepal. What could be the reasons? j. Write the measures to control or adapt to climate change. k. Why should government launch a program to train locals to grow, search, protect, harvest and process herbs? l. Ecotourism is increasing in Nepal. It has created job opportunities for many and raised revenue for the country. However, it has caused some negative impacts on the sites. Enlist a few of them. m. Mustang is a cold region but it is not as cold as it used to be. Snow does not last as longer as it used to. What could be the reason? What could be done to prevent the cause? n. Is it reasonable to use traditional herbs as medicine even though we have modern medicines? 9. Study the given picture and answer the following questions. i. Which plant is shown in the diagram? Write its common name and scientific name. ii. Write any two uses of this plant. iii. Where does it usually grow?

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 161 Key terms and terminologies of the unit 1. 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. Contact force : The force which results due to physical contact of the objects is called contact force. 3. Non-contact force: Non-contact force results even when the interacting objects are not in physical contact. 4. Gravitation: Force of attraction between two bodies in the universe due to their masses is called gravitation. 5. 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.' 6. Universal gravitational constant: Universal gravitational constant (G) is the gravitational force existing between two unit masses which are separated by a unit distance. 7. Gravity : The force with which the heavenly bodies like planets, satellites, etc. pull the objects towards their centers is called gravity. 8. 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. 9. Free fall: The condition in which an objects falls freely only due to the force of gravity is called free fall. 10. Mass: The total quantity of matter contained in a body is called mass. 11. Weight: The force with which the heavenly bodies like planets, satellites etc. attract a mass towards their center is called weight. 12. Weightlessness: When a body is in a state of zero weight, it 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 life UNIT Force and Motion 7 Estimated teaching period Theory Practical 8 2 Sir Isaac Newton is world famous for his contributions to universal gravitation and laws of motion. He was born in England on 4th January 1643 and died on 31st March 1727. He was a mathematician, physicist, astronomer, alchemist and philosopher. He is known for his works in classical mechanics and optics. He with his friend Gottfried Wilhelm Leibniz developed infinitesimal calculus. Sir Isaac Newton About the Scientist

162 foRce and motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Introduction Force is necessary to perform various activities in our daily life. For example, pull, push, stretch, squeeze, etc. are done with the help of force. Generally, force denotes two actions, viz. pull and push. So, 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. Force is a vector quantity. Its SI unit is newton (N) and CGS unit is dyne. One newton is equal to 105 dynes. FACTS WITH REASONS Astronauts in ISS or in the satellite feel weightless, why? Astronauts in the ISS(international space station) or in the satellite move with the high velocity without any external resistance . They are at free fall. So, they feel weightless. On the basis of physical contact, forces can be classified into two categories, viz. contact force and non-contact force. The force which results due to physical contact of the objects is called contact force. Examples of contact force are frictional force, muscular force, etc. Non-contact force results even when the interacting objects are not in physical contact. Gravitational force is a type of non-contact force. The sun and the planets exert a gravitational pull on each other despite their large spatial separation. Electric force, magnetic force, etc. are also examples of non-contact force. In this unit, we will study about gravitation, gravity, acceleration due to gravity, free fall, weightlessness, etc. Gravitation We 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. According to Newton, every object in this universe attracts every other object with a certain force called force of gravitation. Thus, the force of attraction between two bodies in the universe due to their masses is called gravitation. Gravitational force F F Sun Earth Moon Gravitational pull Magnitude of the gravitational force depends upon two masses and the distance between their centers. It is always attractive. Electrostatic force depends upon the strength of two charges and the distance between them. It may be attractive or repulsive. MEMORY TIPS The four fundamental forces of nature are the frictional force, gravitational force, electromagnetic force and nuclear force. The gravitational force of attraction is the weakest force among these. MEMORY TIPS According to Geocentric theory, the solar system revolves around the earth. MEMORY TIPS According to Heliocentric theory, the solar system revolves around the sun. MEMORY TIPS

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 163 depends upon masses of the objects and distance between them. Effect of gravitational force cannot be detected easily in case of two small masses. However, the effect of gravitational force can be seen easily when one of the bodies is very big with large mass. Matters on the earth are affected by the gravitational pull of the sun and the moon. This pulling force is easily noticeable in liquids than solid. FACTS WITH REASONS The effect of gravitational pull of the sun and moon is more in liquids on the earth, why? In solids the molecules are tightly packed with a strong force of attraction. But the force of attraction is weaker in the molecules of liquids. So, liquid molecules move easily. The same gravitational pull on solids and liquids may cause the liquid to flow instead of change in the shape of the solids. So ,the effect of gravitational pull of the sun and moon is seen in liquids on the earth. Newton's Universal Law of Gravitation In 1687 AD Newton published a law about gravitation known as Newton's universal 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.' The direction of gravitational force is along the line joining the centers of the two bodies. Suppose a body A of mass 'm1 ' and another body B of mass 'm2 ' are at a distance of 'd' from their centers. Now, 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 ∝ m1 m2 ………… (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 ∝ 1 d2 ………… (2) From the relation (1) and (2), we get F ∝ m1 m2 d2 or, F = G m1 m2 d2 [Where G is a constant called universal gravitational constant. Its value is 6.67×10-11Nm2 /kg2 ] F d m1 m2 Distance between two masses (d) Gravitational force (F) Decreases by 2 times Increases by 4 times Increases by 2 times Decreases by 4 times i.e. F ∝ 1 d2 Effect of gravitational pull Earth Moon High tide Low tide Combined gravitational pull of the sun and the moon

164 foRce and motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur FACTS WITH REASONS Newton's law of gravitation is called universal law, why? 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 (the atoms) to huge celestial objects like stars, planets, galaxies, etc. So, Newton's law of gravitation is called universal law. The Universal Gravitational Constant Definition Consider two unit masses separated by a unit distance, i.e. m1 = m2 = 1kg and d = 1m Then, the gravitational force between them, F = G m1 m2 d2 = G 1 × 1 12 = G The universal gravitational constant (G) is the gravitational force existing between two unit masses which are separated by a unit distance. Units of G G = F ×d2 m1 m2 Unit of G = unit of F × (unit of distance)2 unit of mass × unit of mass = N × m2 kg × kg = N m2 kg–2 Thus, the SI unit of G is N m2 kg–2. In CGS system, the unit of G is dyne cm2 g-2. Value of G Long 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 . In CGS system, G = 6.67 × 10–11 × 105 dyne × (100 × 100)cm2 1000 × 1000 g2 = 6.67 × 10–11 × 109 dyne cm2 106 g2 ∴ G = 6.67 × 10–8 dyne cm2 g–2 Properties of G i. 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. FACTS WITH REASONS The 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. F = G 1m 1 kg 1 kg

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 165 Applications of Newton’s Law of Gravitation i. Newton's law helps us to determine the mass of the earth and other heavenly bodies. ii. It helps us to calculate the distance between any two heavenly bodies such as the earth and moon, sun and earth, etc. iii. It is applicable to calculate the orbital period of satellites. iv. It helps in discovering new planets, stars and other heavenly bodies. Solved Numerical 7.1 Calculate 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 m We have, F = G m1 m2 d2 = 6.67 × 10 –11 × 50 × 60 102 = 20,010 × 10-11-2 or, F = 2.001 × 10-13+4 = 2.001 × 10-9 N Therefore, the gravitational force between two students is 2.001 × 10-9 N. FACTS WITH REASONS There is a mutual force of attraction between two students sitting on a bench but they do not move toward each other, why? According to Newton's universal law of gravitation, there is a mutual force of attraction between two students sitting on a bench but they do not move toward each other. This is because the gravitational force between two small masses is very weak in nature. Such weak force is not experienced at all. Solved Numerical 7.2 The 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 m We have, F = G m1 m2 d2 = 6.67 × 10 –11 × 6 × 1024 × 7.4 × 1022 (3.84 × 108 )2 Gravitational force between two bodies is same under constant masses and distance all over the universe. MEMORY TIPS The 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

166 foRce and motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur = 296.148 × 1035 × 10–16 14.745 = 2.008 × 1020 N Therefore, 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 them a) Change in gravitational force between two bodies when their masses change but the distance between them remains constant i) When the mass of one object is doubled Let 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 = Gm1 m2 d2 ………………… (i) When m1 is replaced by 2 m1 , then F' = G2m1 m2 d2 = 2 Gm1 m2 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 doubled According to Newton's universal law of gravitation, the gravitational force between two masses is given by F = Gm1 m2 d2 ………………… (i) When m1 is replaced by 2 m1 and m2 is replaced by 2 m2 , then F' = G2m1 2m2 d2 = 4 Gm1 m2 d2 From equation (i) F' = 4F Therefore, the gravitational force between two masses increases by four times when the mass of both objects is doubled. b) Change in gravitational force between two bodies when their masses remain constant but the distance between them gets changed i) When the distance between two objects is reduced to half Let 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 d m1 m2 d 2m1 m2 d m1 m2 d 2m1 2m2

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 167 between two masses is given by F = Gm1 m2 d2 ………………… (i) When the distance between two objects is reduced to half, i.e. d is reduced to d 2 , then F' = Gm1 m2 2 d 2 = 4 Gm1 m2 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 doubled According to Newton's universal law of gravitation, the gravitational force between two masses is given by F = Gm1 m2 d2 ………………… (i) When the distance between two objects is doubled, i.e. increased from 'd' to '2d', then F' = Gm1 m2 (2d)2 From equation (i) F' = 1 4 F Therefore, the gravitational force between two masses decreases by four times when the distance between them is doubled. Consequences of the Gravitational Force i. Gravitational force is responsible for the existence of the solar system, constellations and galaxy. ii. Gravitational force is responsible for the revolution of planets around the sun. iii. Gravitational force is responsible for the revolution of natural satellites around the planets. iv. Gravitational force is responsible for the formation of tides in the sea. Gravity It 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 d m1 m2 m1 m2 d 2 d m1 m2 2d m1 m2 1. 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 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 Tips

168 foRce and motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur 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) = GMm R2 [ ∵ 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 constant Differences between Gravitation and Gravity. Gravitation Gravity 1. 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 = Gm1 m2 d2 . 2. The force of gravity on a body of mass 'm' is F = mg, where 'g' is acceleration due to gravity. Effects of gravity i. The gravity of the earth holds the atmosphere around its surface. ii. Fall of the rain and snow towards the surface of the earth is due to the gravitational pull of the earth. iii. Force against gravity has to be applied to lift an object to a certain height. iv. Objects falling towards the earth's surface accelerate due to gravity. v. Flowing of rivers, blowing of wind, stability of building, bridges, etc. are due to the force of gravity. Acceleration due to gravity Force 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 Gravity An astronaut uses space capsule connected with a parachute while returning to the earth. As a result, the parachute falls with a constant velocity and astronaut remains safe. MEMORY TIPS An astronaut needs 92 minutes to revolve round the earth from ISS. MEMORY TIPS

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 169 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 REASONS Acceleration 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. ACTIVITY 1 Use 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 + 1 2 gt2 to calculate the value of acceleration due to gravity in each case. When u= 0, h = 1 2 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 = GM R2 Let 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 formula F = GMm R2 ………………… (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 = GMm R2 or, g = GM R2 From this equation, the value of acceleration due to gravity 'g' is independent of the mass, shape and size of the body. R M Earth m The 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 or satellite. MEMORY TIPS

170 foRce and motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Solved Numerical 7.3 The 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 m We have, g = GM R2 or, g = 6.67 × 10 –11 × 6 × 1024 (6.4 × 106 ) 2 = 40.02 × 1024 – 11 40.96 × 1012 = 9.8m/s2 Solved Numerical 7.4 Mass 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 = 1.74×106 m Now, the acceleration due to gravity 'g' is calculated by the formula g = GM R2 = 6.67 × 10 –11 × 7.4 × 1022 (1.74 × 106 ) 2 = 49.358 × 1011 3.028 × 1012 = 1.63m/s2 Solved Numerical 7.5 The 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 Re The acceleration due to gravity of the Jupiter gJ = GJMJ RJ 2 = G319Me (11Re)2 = 319GMe 121Re 2 = 2.636 × ge = 2.636 × 9.8 [ GMe Re 2 = g = 9.8 m/s2 ] or, gJ = 25.83 m/s2 FACTS WITH REASONS 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, why? The acceleration due to gravity of a planet having its mass 'M' and radius 'R' is given by g = GM R2 . It means g ∝ 1 R2 . 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.

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 171 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. 2. The value of 'g' varies from place to place on the earth. 2. The value of G is constant i.e. 6.67×10-11 Nm2 kg-2. 3. 'g' is a vector quantity. 3. 'G' is a scalar quantity. Variation of 'g' a) Variation of 'g' on the surface of the earth The acceleration due to gravity is given by the formula, g = GM R2 Where, 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 ∝ 1 R2 Earth is not a perfect sphere. The radius at the equator is greater than the radius at pole, i.e. Re > R p. 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. FACTS WITH REASONS The objects fall faster at the pole than at the equator, why? The value of acceleration due to gravity at the pole of the earth is 9.83 m/s2 and that at the equator is 9.78 m/s2 . When one object is dropped from a certain height at the pole and another identical object is dropped from the same height at the equator then the velocity of the falling object at the pole increases faster. So the objects fall faster at the pole than at the equator. b) Variation of 'g' with height The 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. The value of acceleration due to gravity decreases with the increase in height from the earth surface. R more R less R more Earth Pole (g=9.83 m/s2 ) Equator (g=9.78 m/s2 ) R h Earth m Relation between g and g' g = GM R2 ........ (i) g' = GM (R + h)2 ........ (ii) g' g = GM (R + h)2 ÷ GM R2 = GM (R + h)2 × R2 GM g' = R2 (R + h)2 × g MEMORY TIPS

172 foRce and motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Solved Numerical 7.6 Mass of the earth is 6 × 1024 kg and its radius is 6400 km. Calculate the value of acceleration due to gravity at the top of the Mt. Everest. Also, calculate the weight of a person of mass 70 kg on top of the Mt. Everest. Solution: Given, Mass of the earth (M) = 6 × 1024 kg Radius of the earth (R) = 6400 km = 6400000 m Height of Mt. Everest (h) = 8848 m The acceleration due to gravity at height 'h' from the earth surface is given by g' = GM (R + h)2 = 6.67 × 10–11 × 6 × 1024 (6400000 + 8848)2 = 40.02 × 1013 4.107 × 1013 = 9.74 m/s2 The value of acceleration due to gravity at the top of the Mt. Everest is 9.74 m/s2 . Again, the acceleration due to gravity (g') = 9.74 m/s2 Mass of the person (m) = 70 kg Weight of the person (W) = ? From the formula, W = m× g = 70 × 9.74 = 681.8 N Therefore, the weight of the person of mass 70 kg on top of the Mt. Everest is 681.8 N. FACTS WITH REASONS The 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)2 When 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 depth The value of acceleration due to gravity decreases as we go below the earth surface. It becomes zero at the center of the earth. g' ∝ 1 (R – h)2 The 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

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 173 Mass and Weight ACTIVITY 2 1. 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. Mass The 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. Weight The 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 gravity or, W = m × g The 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 REASONS It is easy to lift a lighter object than a heavier one, why? At a particular place on the earth, the value of acceleration due to gravity is constant. The weight of an object is directly proportional to its mass, i.e. W ∝ m . It shows that a lighter object is attracted with less force and the heavier object is attracted with more force. So, it is easy to lift a lighter object than a heavier one. Variation in weight of a body due to the change in acceleration due to gravity The 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 REASONS Weight 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.

174 foRce and motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Variation in weight of an object when it is carried from the equator to the pole of the earth Acceleration 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. FACTS WITH REASONS The 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 surface The 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)2 As 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 moon The 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 = 1 6 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 REASONS A 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. A person who can jump 1 m on the earth can jump about 6 m on the moon, why? The value of acceleration due to gravity of the moon is almost 6 times less than that of the earth. So, a person who can jump 1 m on the earth can jump about 6 m on the moon. In Nepal, weight (W) as well as acceleration due to gravity(g) is maximum in Kechana kawal (Jhapa). MEMORY TIPS

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 175 Solved Numerical 7.7 A 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/s2 The 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 earth mm × gm = me × ge or mm = me × ge gm = 50 × 9.8 1.63 = 300.61kg The mass that can be lifted by the man on the moon is 300.61 kg. Differences between mass and weight. Mass Weight 1. 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 Fall When we drop a body freely, it falls down due to the effect of gravity. As a result acceleration is produced on it. It is called acceleration due to gravity (g). Thus, when a body is falling only under the effect of gravity without external resistance, the fall of the body is called a free fall. A body falling in a vacuum is an example of a free fall. ACTIVITY 3 1. 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. 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

176 foRce and motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Air resistance affects the acceleration of a falling body. There is more air resistance on the sheet of a paper than that on the paper ball. Due to this reason the sheet of paper falls slowly. But in case of the TT ball and paper ball, they hit the floor simultaneously when there is negligible air resistance. Falling of parachute on the earth is safe because it experiences air resistance which resists the velocity of the parachute. As a result, the parachute falls with the constant velocity without acceleration. More or less same condition also appears in the falling of hail stones, dispersal of hairy seeds, etc. Acceleration produced on a body during free fall is independent of its mass The 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. Robert 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. Conclusion The 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. 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 A folded paper falls faster than an unfolded paper of the same mass when dropped simultaneously from the same height on the earth surface. But they fall together on the surface of the moon as there is no atmosphere. MEMORY TIPS Guinea Air A B Feather Vacuum

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 177 Weightlessness ACTIVITY 4 1. Suspend a piece of stone using a spring balance and hold the spring balance by your hand. 2. Observe the reading of the actual weight on the scale of the spring balance. 3. Now, release the spring balance from your hand. Again, observe the reading during the free fall of the spring balance along with the stone. Does the spring balance show zero reading? Explanation: When the spring balance and stone fall freely with the same acceleration, the stone does not exert force on the spring balance. Thus, the freely falling stone has become weightless. It 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 Satellite When 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 acceleration 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 REASONS A 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 frefall toward the earth produced because of gravitation (centripetal force). Weightlessness in the Space An astronaut in the orbiting spaceship experiences weightlessness. This is because they are within the gravitational field of the earth. The earth's gravity provides necessary centripetal force to keep the spaceship in the orbit. The ship and astronaut have the same acceleration in the space. When the astronaut is in the spaceship orbiting the earth, both the astronaut and the spaceship are in a continuous state of free fall towards the earth’s surface with the same acceleration due to gravity. At the same time, the spaceship does not provide a rigid support to the body of the astronaut. That is why, there is no any reaction force on the body of astronaut. So, an astronaut feels weightless. Weight of a body on the moon is about 1/6 of the weight on the earth. MEMORY TIPS

178 foRce and motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Differences between free fall and weightlessness. Free fall Weightlessness 1. When a body is falling only under the effect of gravity without external resistance, the fall of the body is called a free fall. 1. When a body is in a state of zero weight, it is called weightlessness. 2. Free fall is the cause of weightlessness. 2. Weightlessness is the effect of free fall. Equations of motion for the bodies falling freely under gravity The 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) = 0 For linear motion For vertical upward motion For vertical downward motion v = u + at v = u - gt v = u + gt s = ut + 1 2 at2 h = ut - 1 2 gt2 h = ut + 1 2 gt2 v2 = u2 + 2as v2 = u2 - 2gh v2 = u2 + 2gh Solved Numerical 7.8 A cricket ball is dropped from a height of 10 m. Calculate: i) the speed of the ball when it hits the ground. ii) the time taken to fall through the height 'h'. Solution: Given Height of the ball (h) = 10 m Initial velocity of the ball (u) = 0 Final velocity of the ball (v) = ? i. For a freely falling body ii. Using the equation of motion, v2 = u2 + 2gh v = u + gt or v2 = 0 + 2 × 9.8 × 10 or, 14 = 0 + 9.8 × t ∴ v = 14 m/s ∴ t = 14 9.8 = 1.42 seconds

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 179 HOT SKILL HIGHER ORDER THINKING SKILL 1. Ramanandan Shai thought buying apples in Humla and selling them in Terai using digital balance would make a profit. Is it true? Give scientific reasons. Buying apples in Humla and selling them in Terai using digital balance would not be profit. It is because digital balance measures the mass of apples. The mass of any substance is constant. So, a kilogram of apples in a mountain will still be a one-kilogram apple in Terai. 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. The net reaction force acting on our body will be less than it should be. So, our body feels lighter. We feel like falling, flying or sleepy. Hence, we feel uneasy. 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. 5. If the earth is compressed to the size of the moon what would happen to the acceleration due to the gravity of the new earth? If the earth is compressed to the size of the moon, the mass of earth remains same but its radius will be equal to that of the moon, as a result, acceleration due to gravity must increase. Here, Mass of the earth be M = 6 × 1024 kg Radius of the earth when compressed to the size of moon = 1.74 × 106 m Acceleration due to gravity =? Using formula, g = GM R = 6.67 × 10–11 × 6 × 1024 (1.74 × 106 )2 = 40.02 × 10–11 + 24 4.107 × 1012 = 13.218 × 10-11 + 24 - 12 = 13.218 × 10 = 132.1 m/s2 6. The fall of a parachute towards the earth’s surface is not a freefall. Freefall is a condition when no force acts on a falling object except gravity. When a parachute is falling into the earth, the upthrust of air will oppose its fall. So, it is not a freefall. 7. Under what situation does gravitational force become equal to the gravitational constant? The gravitational force equals the gravitational constant when both of the masses are 1 kg each separated by a 1meter distance. 8. A squeezed paper falls faster than a flat paper if dropped from the same height on earth. A squeezed paper falls faster than flat paper if dropped from the same height in the earth because the

180 foRce and motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur squeezed paper has a small total surface area so it experiences less air resistance. However, the flat paper has more total surface area, so it experiences more air resistance. 9. If an object has twice the mass and twice the radius of the earth, what would be the magnitude of the acceleration due to gravity on that object? Let the mass of the earth is M. Let the radius of the earth is R. Then acceleration due to the gravity of the earth will be g = GM R2 If an object has twice the mass and twice the radius of the earth then, Its mass will be 2M and its radius will be 2R. So, its acceleration due to gravity will be g’ = G2M (2R)2 = 2GM 4R2 = GM 2R2 = 1 2 g ( g = GM R2 ) If an object has twice the mass and twice the radius of the earth then, its acceleration due to gravity will be equal to half of the earth. 10. 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. 3 STEPS 3 STEPS EXERCISE EXERCISE STEP1 1. Select the best answers from the given alternatives a. How many dynes are equal to a newton? i. 10 dynes ii. 100 dynes iii. 1000 dynes iv. 100000 dynes b. What is the force produced because of the masses of the objects? i. magnetic force ii. density iii. gravitation iv. electrostatic force c. 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 d. What happens to acceleration due to gravity if an object moves away from the surface of the earth? i. acceleration due to gravity is always 9.8 m/s2 ii. acceleration due to gravity increases

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 181 iii. acceleration due to gravity decreases iv. acceleration due to gravity does not change e. Which part of the earth has the maximum weight of an object? i. pole of earth ii. equator iii. inside the earth iv. away from the earth f. If the weight of an object on earth is 100 N, how much does it weigh on the moon? i. 100 N ii. 10.20 N iv. 17.04 N iv. 16.7 N 2. Define the following terms with required examples. a. Contact force b. Gravitation c. Gravitational constant d. Gravity e. Mass f. Weight g. Weightlessness h. Free fall i. Weightlessness in space j. Acceleration due to gravity k. Newton's universal law of gravitation. 3. Answer the following questions in very short. a. Write down the relation of the gravitational force between two bodies with their masses and distance between them. b. Which force is responsible for the moon revolving around the earth? c. Write the mathematical relation of Newton's law of gravitation. d. Write the formula of the gravitational force between two bodies of masses 'x' and 'y' kept at a distance 'r'. e. Write the SI unit of the following: i. Gravitational force ii. Gravitational constant iii. Gravity iv. Acceleration due to gravity f. Who calculated the value of G practically for the first time? g. In the formula g = GM R2 , what do G, M and R represent? h. Name two factors on which the acceleration due to the gravity of a planet depends. i. What is the value of acceleration due to gravity at the pole, the equator and the centre of the earth? j. How much is the weight of a 1 kg mass at the pole and the equator of the earth? k. Name two factors on which the weight of a body depends. l. Write the relation between the mass and weight of a body. m. Who performed the coin and feather experiment? n. Write the relation between acceleration due to gravity and the radius of a planet. o. Write the conclusion of the coin and feather experiment. p. If the gravitational force acting on a 75 kg object at 6400 kilometres away from the centre of the earth is 735 N, what would be the weight of that object? q. Write the nature of newton’s law of gravitation. r. What will be the acceleration of a freely falling object on earth? s. What are the conditions required for an object to be in freefall?

182 foRce and motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur STEP2 4. Give reasons. a. Newton's law of gravitation is also called a universal law. b. Gravitational constant is called a universal constant. c. A stone released from our hands falls towards the earth. d. If 1 kg and 10 kg spherical metallic balls are dropped from the same height on the moon, then they reach the ground at the same time. e. Value of 'g' varies from place to place on the earth. f. Value of 'g' is greater at the poles of the earth than that at its equator. g. Weight of a body is found less at the top of the mountain than at its bottom. h. Weight of an object is greater in the polar region than that in the equatorial region of the earth. i. If a body is dropped from the same height once in the equator and then in the polar region, in which place will it fall faster? Explain with reason. j. Fall of a parachutist is not safe on the moon. k. A satellite does not need fuel to go around the earth in its fixed orbit. l. Weight of a person is less inside the deep caves. m. The probability of getting hurt is more when jumped from a taller place. n. A coin and a feather dropped in a vacuum reach floor together but not outside the vacuum chamber. o. Mass of an object on earth is same even when it is measured in Jupiter. p. It is more difficult to lift a 20 kg stone than a 10 kg stone. q. Acceleration in a straight line motion is inversely proportional to the mass of the object but acceleration due to gravity does not depend upon mass of the object. 5. Differentiate between the following. a. Universal gravitational constant (G) and acceleration due to gravity (g). b. Gravitational force and gravity c. Mass and weight d. Free fall and weightlessness 6. Answer the following questions in short. a. The relation of the gravitational constant is given as G = Fd2 m1 .m2 . If the distance between two masses is increased, will the value of G increase, decrease or remains constant? Write in short. b. The acceleration due to gravity on the surface of the earth is 9.8 m/s2 . What does it mean? c. What are the factors affecting acceleration due to gravity? Does it depend upon mass of the object? d. Compare the gravitational force between two bodies with the original gravitational force if: i) the distance between them is doubled. ii) the distance between them is halved.

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 183 iii) the distance between them is halved and both their masses are doubled. e. Does the value of acceleration due to gravity vary from planet to planet? Explain. f. How does the weight of a body vary when it is moved from the equator of the earth to its pole? g. How does the value of 'g' vary as you go: i) above the earth's surface? ii) below the earth's surface? h. Write the conditions of weightlessness. i. Write the difference between the fall of a parachutist on the earth and the moon. j. Write down the effects of gravitation. k. Do the mass of an apple change when brought from Jomsom to Kathmandu? What happens to the weight? l. Even though Jupiter is 317 times heavier than the earth, its acceleration due to gravity is only 2.4 times more than the earth. Explain the possible causes. STEP3 7. Answer the following long questions. a. Observe the given figure and find the gravitational force between m1 and m2 . [Ans: 4 × 10-6 N] b. Observe the given figure and find the gravitational force between m1 and m2 . [Ans: 1.67 × 10-6 N] c. Find the weight of the body shown in the given figure. [Ans: 24.5 N] d. What change occurs in the gravitational force between the sun and the earth when the earth shifts from position P to Q on its orbit around the sun? Write with reason. e. 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. f. Derive a formula for the calculation of the gravitational force exerted by a body of mass m1 on another body of mass m2 separated by a distance 'd'. 2m m1 = 6 kg m1 = 4 kg 20 cm 20 kg 10 cm 50 kg h = 6400 km 10 kg R= 6400 km Earth P Q Earth

184 foRce and motion Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur g. Derive a formula for the calculation of acceleration due to the gravity of a planet having mass 'M' and radius 'R'. 'Or' Derive a formula to show that acceleration due to gravity is independent of the mass of the falling body. h. Explain an experiment to show that the acceleration due to gravity does not depend upon the mass of the falling object. i. What would happen to the acceleration due to the gravity of the earth if it could be compressed to the size of the moon? Explain. j. Draw the diagram i. to show the gravitational force of 6.67 × 10-11 N between two bodies. ii. to show the coin and feather experiment. 8. Numerical Problems a. Calculate the force of gravitation between two objects of masses 50 kg and 120 kg respectively, kept at a distance of 10 m from one another. [Ans: 4.02 × 10-9 N] b. 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] c. The moon is 3×105 km away from Nepal and the mass of the moon is 7 × 10 22 kg. Calculate the force with which the Moon pulls every kilogram of water in our rivers. [Ans: 5.188 × 10–5 N] d. Acceleration due to gravity on the earth is 9.8 m/s2 . Calculate the mass of the earth assuming that it is a sphere with a radius of 6.4 × 106 m. [Ans: 6.018 × 1024 kg] e. The mass and the radius of Jupiter are 1.9 × 10 27 kg and 7.1 × 107 m, respectively, find out the acceleration due to gravity on it. [ Ans: 25.13 m/s2 ] f. 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 1.7×106 m. Find the acceleration due to gravity on the new earth. What will be the weight of a 100 kg mass on that earth? [Ans: 138.48m/s2 13,848 N] g. If the mass of the moon is 7.2× 1022 kg and its radius is 1.74 × 106 m, calculate the value of acceleration due to gravity on the moon. Find the weight of a person with a mass of 60 kg on the moon. [Ans: 1.63 m/s2 , 97.8 N] h. The mass of the earth is 6 × 1024 kg and its radius is 6400 km. Calculate gravitational force between earth and a unit mass on its surface. Calculate the value of acceleration due to gravity at top of the Mt. Everest. [Ans: 9.8 N, 9.74m/s2 ] i. The radius of the earth is 6400 km and its mass is 6 × 1024kg, what will be the value of acceleration due to gravity at a distance of 3600 km far from the earth's surface? [Ans: 4.002 m/s2 ]

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 185 j. If an object at a distance of 6,400 km from the centre of the earth weighs 10N, what will be its weight if it is lifted to 12,800 km from the centre of the earth? [Ans: 2.5 N] k. If a weight lifter can lift 100 kg mass on the earth, what mass can he lift on Jupiter, if the acceleration due to gravity on Jupiter is 25.13 m/s2 ? [Ans: 38.997 kg ] l. A student drops a stone into a river from the bridge. If he heard the sound of the collision of the water surface and the stone after 2 seconds, calculate the height of the bridge from the water surface. [Ans: 19.6 m] m. 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 ] n. 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 × 107 m] o. The gravitational force between two masses at a distance of 6.4 × 106 m is 500 N. What should be the distance between them to increase the gravitational force by two times? [ Ans: 4.525 × 106 m ] p. If acceleration due to gravity at the earth is 9.8 m/s2 , how much would be the acceleration due to gravity at the moon whose mass is 7.35 × 1022 kg and radius is 1.74 × 106 m. q. The gravitational force between the earth and the sun is 3.5 × 1022N. If the mass of the sun and the earth is 2 × 1030 kg and 6 ×1024 kg respectively, calculate distance between them. r. When a ball was thrown upward, it gained maximum height of 20 meters. Calculate the time required to reach that height and also find the initial velocity of the ball.

186 PReS SuRe Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Key terms and terminologies of the unit 1. 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. Introduction We 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 UNIT Pressure 8 Estimated teaching periods Theory Practical 4 1 Archimedes of Syracuse is well known for Archimedes principle developed to find the volume of irregular solids which could be used to find the purity of metals. He was born in Ancient Greece, the ancient city of Syracuse in Sicily in 287 BC and died in 212 BC. He was a Greek mathematician, physicist, engineer, astronomer and inventor. He discovered the centre of gravity, the law of lever and Archimedes’ screw. Archimedes of Syracuse About the Scientist

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 187 Pressure (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-2 or pascal (Pa). To increase pressure we should increase the force applied and decrease area. FACTS WITH REASONS A 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) Pressure 1. 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 REASONS Pressure 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 pressure The solid molecules are very compact. The intramolecular space in solid is very low. The molecules of solid do not move like the molecules of liquid and gas. So, pressure does not transmit through solid. In case of liquid and gas, the intra-molecular space is more than solid. These molecules move from one place to another. Therefore, the liquid and gas together is called fluid. Pressure transmit in all direction through fluid (liquid and gas). Liquid Pressure Liquid 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 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 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 TIPS

188 PReS SuRe Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur 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 1 a) 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 Pressure a) Liquid applies pressure in all directions Liquids 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. b) Pressure increases with depth At a point in greater depth, the weight of liquid above the point increases. This causes high pressure. FACTS WITH REASONS In 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. c) Pressure does not depend upon the shape of the container Whatever the shape or width, the liquid pressure at a particular depth is the same. d) Pressure depends on the density of the liquid The liquid with more density applies more pressure at a particular depth than the liquid with less density. Factors on which the pressure at a point in liquid depends The pressure due to a liquid depends up on three factors, viz. depth of the liquid, density of the liquid and acceleration due to gravity at that place. a) Liquid pressure is directly proportional to its height. ( i.e. p ∝ h) Liquid pressure Liquid in different shape container

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 189 FACTS WITH REASONS Dams are made thicker at the bottom, why? Water is collected in dam. The water pressure increases with the depth. More pressure results more pushing force at the bottom of a dam. So, the dams are made thicker at the bottom to withstand the higher pressure of water. b) Pressure in a liquid is directly proportional to its density. ( i.e. p ∝ d) FACTS WITH REASONS If out of two identical bottles, one is filled with water and another is filled with oil, then the bottom of the bottle filled with water experiences more pressure, why? A liquid with more density exerts more pressure at the bottom of the container. The density of water is higher than that of oil. So, if out of two identical bottles, one is filled with water and another is filled with oil, then the bottom of the bottle filled with water experiences more pressure. c) Pressure in a liquid is directly proportional to acceleration due to gravity. ( i.e. p ∝ g) FACTS WITH REASONS When a tank filled with water is carried from terai region to the Himalayan region then the pressure at its bottom decreases, why? The acceleration due to gravity decreases with the increasing altitude from the sea level. When a water tank filled with water is carried from terai region to the Himalayan region, the value of acceleration due to gravity becomes less. This causes a decrease in the pressure at the bottom of tank. Transmission of Liquid Pressure: Pascal's Law In 1650, Pascal formulated a very useful law concerning transmission of liquid pressure. 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". Verification of Pascal's law Verification of Pascal's law can be done with a simple experiment. Take a polythene bag and fill with water. With the help of a needle make a number of holes all around the bag. Now, squeeze the bag as shown in the figure. It can be seen that water comes out through all the holes simultaneously with the same pressure. We can verify Pascal's law in another way, too. Take a spherical vessel completely filled with water and fitted with four water tight pistons having the same cross-sectional area. When a piston is pressed, then all other pistons experience equal pressure and move outward equally. It shows that liquid pressure transmits equally in all directions. Applications of Pascal's law Pascal's law has a number of practical applications in our daily life. Some of them are hydraulic press, hydraulic jack, hydraulic brakes, etc. In these devices, there is multiplication of force on the basis of Pascal's law. Polythene bag Water Transmission of pressure Q S R P Spherical glass vessel

190 PReS SuRe Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Hydraulic Machines Hydraulic machines are the devices which multiply force on the basis of Pascal's law. There are different types of hydraulic machines like, hydraulic jack, hydraulic press, hydraulic brake, hydraulic lift, etc. While working, hydraulic machines use following properties of liquids: i. Liquids are incompressible. ii. Liquid transmits pressure equally and perpendicularly in all directions. Construction Hydraulic machines consist of cylinders of different crosssectional area. These cylinders are connected with a pipe and filled with a liquid. Let there be two pistons of cross-sectional area A1 and A2 . Multiplication of force Suppose a force (F1 ) is applied on the small piston of the cross-sectional area (A1 ). This force exerts an external pressure on the enclosed liquid which is given by the formula, P1 = F1 A1 . This pressure transmits equally in all directions. The pressure (P1 ) exerts a force (F2 ) on the large piston of the cross-sectional area (A2 ) which is given by the formula, P2 = F2 A2 . From Pascal's law, P1 = P2 or, F1 A1 = F2 A2 or, F2 A2 = F1 A1 or, Large force on piston B Large cross-sectional area = Small force on piston A Small cross-sectional area or, F2 = A2 A1 × F1 When A2 > A1 , F2 > F1 , it means that the large piston experiences many times bigger force than the force applied on the small piston. So, a hydraulic machine is also called a force multiplier. FACTS WITH REASONS Hydraulic machine is called a force multiplier, why? According to Pascal's law, pressure on the small piston = Pressure on the big piston i.e. P1 = P2 i.e., F1 / A1 = F2 / A2 or, F1 × A2 = F2 × A1 Since, A2 > A1 , thus, F2 > F1 Hence, a hydraulic machine is a force multiplier. Hydraulic machine The principle of a hydraulic machine states, "A large force is developed on a larger piston when a small effort is applied on the smaller piston." MEMORY TIPS Liquid used in hydraulic machine should be incompressible or non-combustible. MEMORY TIPS

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 191 Different Types of Hydraulic Machines i) Hydraulic jack Hydraulic jack is a device which is constructed on the basis of Pascal's law. With the help of a hydraulic jack it is easier to raise a load like trucks, buses, cars, etc. It consists of two pistons of different diameters. When a small effort is applied on the small piston, a large force develops on the larger piston. It is used for servicing automobiles in service centers. ii) Hydraulic brakes Hydraulic brakes are the applications of the Pascal's law. They are used in heavy automobiles like motorbikes, cars, buses, trucks, aeroplanes, etc. to stop them by applying a small effort. The construction of hydraulic brakes to multiply effort is as shown in the given figure. As the brake pedal is pressed, the piston of the master cylinder increases pressure inside the tube containing brake oil. The brake oil transmits pressure equally in all directions. Through the brake oil, pressure spreads to the wheel cylinder. As the wheel cylinder has large cross section area, it magnifies force. Now, the large amount of force is applied on the brake shoes and wheel rim. Finally, the friction between brake shoes and wheel rim slows down the wheel and vehicle stops. iii) Hydraulic press Hydraulic press is an application of Pascal's law. It is used for compressing cotton bales, extracting oil from oil seeds, punching holes in metals, giving specific shapes to metal sheets, etc. The construction of hydraulic press is shown in the given figure. When effort is applied from the force pump, a large force is developed on the large piston. It pushes the load upward. The load is pressed in between piston and rigid ceiling as shown in the given figure. iv) Hydraulic lift Hydraulic lift is a device which is constructed on the basis of Pascal's law. With the help of a hydraulic lift it is easier to raise a load like chair, bed, etc. in the hospital. Similarly, it is used to lift the load like cars in the car servicing Hydraulic jack Liquid F2 Valve 1 Valve 2 Applied force F1 Foot pedal Liquid Piston Pipeline To other wheel Brake shoe Hinge Return spring Brake-shoe Wheel cylinder Master cylinder Hydraulic brakes cotton ball a1 a2 f1 Hydraulic Press

192 PReS SuRe Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur centre. Hydraulic lift consists of two pistons of different diameters. When a small effort is applied on the small piston, a large force develops on the larger piston. Solved Numerical 8.1 Answer the following questions on the basis of the given figure. i) Which equipment is shown in the figure? On the basis of which law does it work? ii) According to the figure, calculate the pressure exerted at A. iii) Calculate the effort (F2 ) on piston B. Solution: i) The equipment shown in the given figure is a hydraulic machine. It works on the basis of Pascal's law. ii) Given, Force on piston A (F1 ) = 240 N Area of piston A (A1 ) = 20 cm2 = 20 × 10-4 m2 [ 100 cm = 1m] We know, P1 = F1 A1 = 240 20 × 10– 4 = 1.2 × 105 Pa ∴ Pressure at A ( P1 ) = 1.2 × 105 Pa iii) Effort on piston B (F2 ) = ? Area of piston B (A2 ) = 0.4 m² We know, F2 × A1 =F1 × A2 or, F2 = F1 A2 A1 = 240 × 0.4 20 × 10–4 = 4.8 ×104 N ∴ Effort on piston B (F2 ) = 4.8 ×104 N Solved Numerical 8.2 The ratio of the area of cross-section of the two pistons in a hydraulic machine is 1:15. Calculate the force that should be applied on the narrow piston to overcome a force of 1200 N on the larger cross-section piston. Solution: Given, Ratio of the cross-section of the two pistons, A1 : A2 = 1: 15 Force on the larger cross-section piston (F2 ) = 1200 N Force required on the narrow piston (F1 ) = ? From Pascal's law, F1 A1 = F2 A2 or, F1 = F2 A1 A2 = 1200 × 1 15 = 80N The force that should be applied on the narrow piston is 80 N. 0.4 m2 240N F2 = ? A B 20 cm2 The tendency of a liquid to exert an upward force on an object placed in it is called buoyancy and the resultant upward force of a liquid is called buoyant force. MEMORY TIPS

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 193 Upthrust When we push a wooden cork in water, then the cork immediately rises up to the surface. In another example, it is easy to pull a bucket full of water when it is inside the well water. From these two examples, it is clear that the objects appear to be lighter inside water. It is due to the upward force exerted by the water. The same feeling can be experienced in other liquids, too. So, every liquid exerts an upward force on the object immersed in it. This upward force is called upthrust. Thus, the resultant upward force acting on an object when partially or wholly immersed in a liquid is called upthrust. Causes of upthrust In the above figure, a cubical object is kept in water. It experiences force from all directions. The force applied from right and left of the cube is equal and opposite. The pressure and force applied from down to up is greater than the pressure and force applied from up to down. This resultant force is called upthrust. It is always in upward direction. Thus, the difference in depth between upper surface and lower surface of the object has different pressure and thrust. This is the main cause of upthrust. ACTIVITY 2 To prove that a solid weighs less in water and more in air. 1. Take a stone and tie it to a string as shown in the given figure. 2. Fix another end of the string with a spring balance. 3. Measure the weight of the stone in air and in water. Do you find a difference in weight? Apparent loss in weight of an object in liquid is equal to the upthrust, i.e. Upthrust = weight in air – weight in liquid In the figure shown above, upthrust = 8 N – 6 N = 2 N. 8N 6N Factors Affecting upthrust Following factors affect upthrust. i) Density of the liquid Upthrust is directly proportional to the density of the fluid in which an object is immersed. That is, Upthrust ∝ density of the fluid. For example, the cork dips more easily in oil than in water. Similarly, an iron nail floats in mercury but sinks in water. This is because mercury has more density and exerts more upthrust. Upthrust (U) ∝ density of the liquid (d) Upthrust Small forces on the top Water Large forces on the bottom Weight of box Upthrust is applicable both in liquid and gas. The combined word of liquid and gas is called fluid. MEMORY TIPS Dead Sea float: The Dead Sea is a salt lake. It is more than 400 m below the sea level. Density of pure water is 1000 kg/m3 but the density of Dead Sea water is 1170 kg/m3. So, it is very easy to float in Dead Sea. MEMORY TIPS

194 PReS SuRe Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur ACTIVITY 3 To prove that an egg sinks in pure water and floats in salty water. 1. Take two drinking glasses and fill with water almost to the top. 2. Gently drop an egg in each glass. They sink right to the bottom. 3. Take out the eggs from the glasses and add about four teaspoons of common salt in a glass and stir. 4. Gently drop an egg into the salt solution. Observation: The egg floats in salt solution. Explanation: Density of the salt solution is more than that of pure water. Therefore, the salt solution exerts more upthrust on the egg and it starts to float. Egg Egg Salt Water solution Pure Water FACTS WITH REASONS It is easier to swim in the sea water, why? Upthrust is directly proportional to the density of the liquid. Sea water has a greater density than river water. Thus, upthrust experienced by a swimmer in sea water is comparatively more than in river water. So, it is much easier to swim in the sea water. The weight of an object in air is more than that in water, why? Upthrust is directly proportional to the density of the fluid. Density of air is less than that of water. The upthrust due to air is negligible in comparison to the upthrust due to water. So, the weight of an object in air is more than that in water. ii) Volume of the fluid displaced Upthrust is directly proportional to the volume of the fluid displaced by the object. That is, Upthrust (U) ∝ volume of the fluid displaced (V) It means, the larger the volume of a body submerged in a fluid, the greater is the upthrust. FACTS WITH REASONS It is easy to immerse a small empty airtight plastic bottle into water than a bigger empty plastic bottle, why? Upthrust is directly proportional to the volume of liquid displaced by the body. A big airtight plastic bottle displaces more volume of water than a small plastic bottle. It creates more upthrust on the bigger plastic bottle. So, it is easy to immerse a small empty airtight plastic bottle into water than a bigger empty plastic bottle. iii) Acceleration due to gravity The upthrust is directly proportional to the acceleration due to gravity. i.e., Upthrust (U) ∝ acceleration due to gravity (g) Archimedes' Principle Experimental study of the upthrust on a body was first carried out by Greek Scientist

Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Modern Concept Science & Technology - 10 195 Archimedes. The conclusion drawn from his experiment is known as 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". If the volume of the body inside the liquid is 'V' and the density of liquid is 'd', then the upthrust is given by Upthrust (U) = Weight of the liquid displaced = mg = Vdg Experimental Verification of Archimedes' Principle Take a stone and tie it to a fine cotton thread. Suspend it from the hook of spring balance. Record the weight of the stone in air. Let the weight of the stone in air be 'W1 '. Take a Eureka can (overflow jar) and place a clean beaker under its spout. Let the weight of the beaker be 'W3 '. Pour water in the overflow jar till it starts overflowing from spout. Immerse the stone in water and measure its weight. Let it be 'W2 '. Finally record the weight of the beaker with water. Let it be 'W4 '. Calculate upthurst and weight of the water displaced by the stone. Upthrust = W1 - W2 Weight of the water displaced = W4 – W3 Do you find the upthrust equal to the weight of the water displaced? Solved Numerical 8.3 Answer the following questions from the given figure. i. How much is the upthrust exerted on the object immersed in water? ii. Calculate mass of the water displaced. Solution: i. Given, weight of the object in air (W1 ) = 60 N Weight of the object in water (W2 ) = 50 N Now, upthrust on the object (U) = W1 - W2 = 60 - 50 = 10 N ii. According to Archimedes' principle, "Eureka" comes from the Ancient Greek word. Its meaning is "I have found (it)". MEMORY TIPS Spring balance Stone Water Top pan balance Beaker Ureka can W2 W1 Verification of Archimedes' principle Upthrust is equal to the apparent loss of weight of the submerged object. MEMORY TIPS Weight of an object in air > in water > in salt solution MEMORY TIPS Stone Water 50N 60N

196 PReS SuRe Approved by the Curriculum Development Centre, Sanothimi, Bhaktapur Weight of the liquid displaced = upthrust Mass of water displaced × g = 10 ['g' is the acceleration due to gravity] ∴ Mass of the water displaced = 10 9.8 = 1.02 kg FACTS WITH REASONS How do we know the purity of the ornaments? Each metal has its own density. While making ornament if any impurity is mixed in it, the ornament has more or less density and volume compared to the pure metal. As a result, the ornament displaces liquid more or less than the volume of pure metal of the same weight. Principle of Flotation A wooden cork floats in water but a piece of stone sinks. It is because the wooden cork has less density than water but the stone has more. Sinking and floating do not depend upon density of the liquid only. But they also depend upon the weight of the liquid displaced. According to law of floatation, "a floating body displaces liquid equal to its weight." Forces Acting on an Immersed Body When a body is immersed in a liquid, it is acted upon by two forces. They are: i. The weight of the body 'W' acting vertically downwards. ii. The upthrust due to the liquid 'U' acting vertically upwards. These two forces are acting just opposite of each other. The movement of the body is in the direction of the resultant force. There are three possible conditions: i. When the weight of the body is greater than upthrust (i.e. W> U) : The downward force on the body becomes more and the resultant force acts downward. As a result, the body sinks in the liquid. Density of a body > Density of liquid ii. When the weight of the body is equal to the upthrust (i.e. W = U) : The downward force on the body is balanced by the upward force. Thus, the resultant force on the body becomes zero. In this condition, the body floats freely under the liquid surface. In this condition, the weight of the displaced liquid is equal to the weight of the body. This condition is satisfied when the density of the body is equal to the density of the liquid. Density of a body = Density of liquid iii. When the weight of the body is less than the upthrust (i.e. W < U) : The upward force on the body becomes more and the resultant fore acts upward. In this condition, the body floats partially immersed. This condition is satisfied when density of the body is less than the density of the liquid. Density of a body < Density of liquid