Oasis School Science and Technology 10 New

Oasis School Science and Technology - 10 151 p. Pulmonary circulation q. Blood pressure r. Systolic blood pressure s. Diastolic blood pressure t. Heart beat u. Pulse v. Diabetes w. Angiography 3. Answer the following questions in very short. a. What are the components of blood? b. What is the function of haemoglobin? c. Name the blood vessels that carry pure blood to the left auricle and impure blood to the right auricle of the heart. d. Which blood vessel carries impure blood from the heart to the lungs? e. Where are the aortic valve and pulmonic valve located? f. What is the blood pressure of a healthy young adult? g. Name the device which is used for measuring blood pressure. h. What is heart bypass surgery? i. Where is the saphenous vein harvested from? j. Which treatment technique for heart attack uses X-rays? k. What happens if RBC count is too low in the body? l. How many chambers are there in the heart? Write their names. m. How many valves are there in human heart? Write their names. n. What antigens are present in blood group A? o. What makes the blood red? p. What is the cause of difficulty in blood clots? q. Which blood cell is amoebic in shape? r. Which blood cells do not have a nucleus? s. Which technology is suited for detecting a blockage in coronary arteries? 4. Give reasons. a. Anaemic person feels very tired. b. WBC helps to prevent diseases. c. WBCs are called soldiers of the body. d. Blood does not clot inside the blood vessels but clots in the wounds. e. Ventricles are bigger and thicker than auricles. f. Left ventricle is bigger and thicker than the right ventricle. g. Veins have valves but arteries do not. h. Arteries are deep-seated and thick. i. Veins are thin and superficial. j. Capillaries are microscopic and very thin. k. Systolic blood pressure is higher than diastolic pressure. l. Right auricle is larger than the left auricle. m. All the arteries carry pure blood but the pulmonary artery carries impure blood. n. Special dye is mixed into the blood through a catheter while performing angiography. o. Sometimes multiple bypass surgery is performed at once.

152 Oasis School Science and Technology - 10 p. Blood group must be identified before blood transfusion. 5. Differentiate between the following. a. Erythrocytes and leucocytes b. Auricles and ventricles c. Bicuspid valve and tricuspid valve d. Pulmonary artery and pulmonary vein e. Artery and veins f. Systemic circulation and pulmonic circulation g. Bypass surgery and angiography 6. Answer the following questions in short. a. Write down the transportation-related function of the blood. b. Draw a neat and clean diagram to show the flow of the blood. c. Write any three characteristics of blood. d. What are the three functions of plasma? e. Name the valves present in between the auricles and ventricles of the human heart. Also, write down their structure and functions. f. What should a patient do before performing angiography? g. What is the function of aspirin? h. How do blood clots at wounds after a few minutes? i. Blood pressure of an adult person is 120/80 mmHg. What does it mean? j. What kind of symptoms can be observed if a person has a low WBC count? k. Will the higher concentration of fibrinogen hamper blood circulation? l. What are the causes and preventive measures of high blood pressure? 7. Answer the following questions on the basis of the given figure. i. What is shown in the given diagram? ii. Name parts A and D. iii. Mention the function of B and C. 8. Answer the following long questions. a. Explain three major functions of blood circulation in the human body. b. Which organs make the circulatory system in human beings? Describe the main components. c. Describe the internal structure of the human heart with a labelled diagram. d. What is an artery? Describe its structure in brief with a neat figure. e. What are veins? Describe the structure of veins in brief with a neat figure. f. Describe blood circulation in human beings with the help of a diagram. g. Write a short note on uric acid and diabetes. Mention their symptoms, causes and preventive measures. h. Draw a figure showing systematic and pulmonary circulation. i. Heart attack is one of the major causes of death throughout the world. What kind of lifestyle leads to a heart attack? Can it be avoided? What should we do A B C D

Oasis School Science and Technology - 10 153 to avoid it? Discuss. j. Why and how is angiography performed? k. Why and how is bypass surgery done? Describe in brief. l. What kind of life style should we live to avoid a heart attack? m. Ram had a heart attack. He survived it. The doctor saved his life. They performed heart bypass surgery on him. How should he live his life from now onward to recover early? n. Study the given flow chart and answer the following: left ventricle > body > right auricle i. What type of blood circulation is it? ii. What blood vessels take blood from the left ventricle to the body? iii. What blood vessels take blood from the body to the right auricle? o. Study the given diagram and answer the following. Blood cells Shape Nucleus A Biconcave Absent B Irregular Present C Round Absent i. Write the name of A, B and C. ii. Low count of which blood cells cause anaemia? iii. Which disease a person suffers from if B is more in number? iv. Which blood cell is lacking if blood does not clot efficiently in the wounds? 9. Study the given diagram of the heart and answer the following questions. i. Write the names of P, T, C and D. ii. Write the function of W and X. iii. What type of blood passes through valve R? Write the name of this valve. iv. Why is the wall of chamber L thicker than the wall of chamber T?

154 Oasis School Science and Technology - 10 Key terms and terminologies 1. Climate : Climate is an average weather condition recorded over a long period of time (usually 30 years). 2. Climate change : Climate change is a regular or irregular alteration in the weather patterns observed over a very long period of time. 3. Endangered animals: Animals or birds whose distribution are limited and are few in number at a given geographical area at that time are called endangered animals. 4. Endangered plants : Plants whose distribution are limited and are few in number at a given geographical area at that time are called endangered plants. 5. Medicinal plants : Medicinal plants can be defined as the plants that possess therapeutic properties or exert beneficial pharmacological effect on the human or animal body. 6. In situ conservation : The conservation of animals and plants by maintaining them in their natural ecosystem in which they occur is called in situ conservation. 7. Ex situ conservation: The conservation of animals and plants outside the natural ecosystem like zoo, botanical garden, zoological park, seed bank, etc. is called ex situ conservation. UNIT 6 NATURE AND ENVIRONMENT Estimated teaching periods Theory 5 Practical 2 • Concept of climate change: cause, effects and control measures • Different kinds of endangered animals in Nepal and their conservation • Importance, identification and uses of medicinal plants The Sequence of Curriculum Issued by CDC Sir Arthur George Tansley is known as a pioneer in the science of ecology. He was born in England on 15th August 1871 and died on 25th November 1955. He is a botanist and ecologist. He introduced the concept of the ecosystem in biology. He was honoured with the Linnean Medal and a Fellow of the Royal Society. He was educated at Highgate School, University College London and Trinity College, Cambridge. About the Scientist Sir A. G.Tansley

Oasis School Science and Technology - 10 155 Climate Climate refers to the average weather conditions that have been recorded over a long period of time (usually 30 years). It is made by keeping data of temperature, rainfall, seasons, humidity, etc., over a long period of time in one place. It is not the same as weather. This is because weather is a temporary condition like raining, windy, cloudy, or sunny. Climate Change The climate of a place does not change much even after many decades, or the changes are hard to notice. The average temperature of the earth's surface remains the same because of this small change. So, it keeps life going on the earth. If the earth's temperature rises by even a small amount, like 2 degrees Celsius, it will be terrible. If we study the climate data since 1880 A.D., it has been found that the change in climate has accelerated. The surface temperature has risen by 1.80 F. It is a bad news. Therefore, climate change is a regular or irregular alteration in the weather patterns observed over a very long period of time. To observe climate change, we need to analyze the statistical data of decades. The average temperature of Nepal has risen by 0.056 degree Celsius due to global warming. Causes of Climate Change It is to be noted that climate continuously changes due to natural causes like solar activity, earthquake, volcano, earth’s rotation etc. But change due to natural cause is very slight. The main problem is anthropogenic causes (human causes). Scientists believe that the greenhouse gases, environmental pollution, deforestation, industrial gases and other human activities are the main reasons behind the change in climate. The major causes of climate change are given below : A. Natural causes of climate change 1. Change in solar activity In the sun, there is a process called thermonuclear fusion. It is the main source of energy on the sun. If the rate of the thermonuclear fusion reaction changes, the amount of solar energy produced also changes. Because of this, it changes the weather on the earth. 2. Change in the reflection and absorption of the sun light The earth and its atmosphere absorbs about 70% of the solar radiation and reflects other. The absorbtion and reflection of the solar radiation depends upon the earth's surface and its atmosphere. If there is more absorption of solar radiation, there is more heat on the earth and changes climate of the earth.

156 Oasis School Science and Technology - 10 3. Volcanic eruption Dust particles and compounds of sulphur are released during volcanic eruption. These substances accumulate in stratosphere and block the solar radiation which results in climate change. Reasonable Fact Volcano causes climate change. Volcano releases lots of hot carbon dioxide, methane and other greenhouse gases which increase temperature of the atmosphere resulting climate change. 4. Increase in temperature Different parts of the earth receive different amount of solar radiation due to geographical variation. The parts of the earth that receive more solar radiation become hotter than the parts that receive less solar radiation. The increase in temperature is one of the causes of change. B. Man-made causes of climate change 1. Release of greenhouse gases Different types of greenhouse gases like carbon dioxide, chlorofluorocarbons, methane, nitrous oxide, ozone, etc. are released in atmosphere due to various human activities. These greenhouse gases are responsible for climate change. 2. 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. Reasonable Fact Use of CFCs in refrigerators, AC should be replaced by ammonia. 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. 3. Deforestation Forests help to maintain balance in amount of carbon dioxide and oxygen in atmosphere as green plants use carbons dioxide gas for photosynthesis. The amount of carbon dioxide gas in atmosphere increases due to deforestation which results in increase in temperature and climate change. 4. Excessive use of chemical fertilizers Greenhouse gases are released due to excessive use of chemical fertilizers. Similarly, overuse of chemical fertilizers makes the land dry. As a result, temperature of the earth increases and change in climate takes place. 5. Agricultural wastes Any waste and its treatment produces a lot of methane gas. Methane gas is a greenhouse gas. Hence it causes global warming.

Oasis School Science and Technology - 10 157 6. Industrialization Various types of gases like carbon dioxide, sulphur-dioxide, etc. are released in atmosphere while running industries. There gases contribute to greenhouse effect which results in change in climate. Effects of Climate Change i. It melts snow in polar region and the Himalayan region. ii. It causes loss of biodiversity. iii. It decreases agricultural production and changes the crop pattern. iv. It increases the level of sea, due to the melting of ice in the polar region. v. It decreases the amount of fresh water. vi. It affects the global water cycle. vii. It changes wind circulation and affects the pattern of rainfall of a particular place. viii. It causes improper distribution of rainfall. Measures of Climate Change Management i. Deforestation should be discouraged and afforestation should be encouraged. ii. Plantation should be done on bare parts of land. iii. The resources of water should be conserved and managed. iv. Overuse of fossil fuels should be reduced. v. Alternative sources of energy should be developed and used. vi. Environment pollution should be minimized. vii. Release of greenhouse gases should be stopped. viii. Use of chlorofluorocarbons should be banned. ix. Proper management of waste materials should be done. x. Natural environment should be conserved. xi. Agriculture system should be improved. xii. Unmanaged development works should be controlled. xiii. Proper use and management of automobiles should be ensured. xiv. Over use of chemical fertilizers should be discouraged. xv. Public awareness should be generated. Activity 1 • Prepare an artificial greenhouse nearby your house by using plastics. • Note down the change in temperature inside and outside the greenhouse. • What can you conclude from this activity? Activity 2 • Study the adverse effects of climate change in your locality. • Find out the causes of climate change in your locality. • Suggest the measures of climate change management. • Prepare a short report and submit to your science teacher.

158 Oasis School Science and Technology - 10 Rare and endangered animals and birds in Nepal Rare animals are the animals which are found few in number in a place and time. The animals which are found in Nepal only are rare for the rest of the world. Similarly, the animals which are found few in number in Nepal and in plenty in other parts of the world are rare for Nepal. Similarly, 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. In Nepal, there are many species of rare and endangered plants and animals. Causes to extinct plants and animals i. Animals and plants will become extinct as a result of climate change and pollution. ii. Animals and plants become extinct as a result of uncontrolled and excessive use. iii. The appearance of new invasive species of animal and plant replace old and traditional animal and plant species. iv. Hunting and smuggling of the animals reduces its number and finally extinct. Examples of some protected mammals in Nepal Some examples of protected mammals in Nepal are given below : Black Buck, Gaur Bison, Wild Yak, Pygmy Hog, Red Panda, 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. Examples of some protected birds in Nepal 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. Examples of some protected reptiles in Nepal Some examples of protected reptiles in Nepal are given below. Gharial, Asiatic rock python, Golden monitor lizard, etc. a. One-Horned Rhinoceros Scientific Name: Rhinoceros unicornis Body Structure: One-horned rhinoceros is one of the protected animals of Nepal. Its length is about 3.8m and the height ranges from 1.1 to 1.7 m. Its weight varies from 2000 to 4000 kg. Its body is covered with thick skin which acts as an armour. There is no hair on its body except in the tail tip and ear fringes. It has brown or grey body colour. There is a horn on its nose. It produces one baby at a time. Habitat: One-horned rhinoceros is found in Terai region of Nepal. It lives in swampy

Oasis School Science and Technology - 10 159 grassland and sal forests of Chitwan and Bardiya National Parks. One-horned rhinoceros is classified by the IUCN Red list of threatened species as 'endagered'. In Nepal, Rhino is poached for its horn, hide and hoof. Food: It feeds on grass, shrubs, foliage and aquatic plants. b. Royal Bengal Tiger Scientific Name: Panthera tigris Body Structure: It has black strips on its yellow to light orange coat. It is about 2.7 m to 3.1 m in length and 1 m in height. Its weight varies from 130 to 200 kg. It produces up to 4 babies at a time. Habitat: It is found in the forest of Terai region. It is found in Chitwan National Park, Bardiya National Park, Parsa Wildlife Reserve and Shukla Phanta Wildlife Reserve. It is also an endangered species. Food: It feeds on vertebrates like Chittal, Wild pig, Deer, Ratuwa, Laguna, etc. life span: Its life span is about 15 years. c. Asiatic Rock Python Scientific Name: Python molurus Body Structure: It is a large snake. Its body is white, black and spotted. Its body is about 7 m long and weight is about 90 kg. It is a non- poisonous snake. It has a series of dark brown and circular spots. It has a wide head and small eyes. Habitat: It is found in dense forest of Terai region. It hides itself in a log of wood and dry leaves. Food: It feeds on small mammals, birds and reptiles. It is also an endangered species. Life span: Its life span is about 19 years. d. Asiatic Elephant Scientific Name: Elephus maximus Body structure: Elephant is the largest land animal. Its height is about 3.5 m. It has a long trunk and two tusks. The tusks of male elephant are larger than that of the female. It produces one baby at a time. Habitat: It is found in dense forest of Terai region. It is found from Jhapa to Kanchanpur. It is also an endangered mammal. It is hunted for its tusks. Food: It feeds on twigs, leaves, grasses, bamboo shoot and grain. Life span: Its life span is about 70 years.

160 Oasis School Science and Technology - 10 e. Red Panda Scientific Name: Ailurus fulgens Body Structure: Red panda is an attractive wild animal which is slightly larger than cat. It has a rounded head, pointed large ears and stumpy muzzle. It has rusty red body colour. Habitat: It is found in the temperate forest at an altitude of about 3000 m. It is generally found in Kanchenjunga and Taplejung. It is an endangered mammal. It is hunted for its attractive furry skin. Food: Its main food is bamboo shoot, grasses, fruits, etc. Life span: Its life span is about 7 years. f. Giant Pied Hornbill Scientific Name: Buceros bicornis Body Structure: It has a long beak. There is yellowish flattened crest above its beak. Its body colour is brownish black. It has a long tail with white colour. Its weight is about 3 to 3.5 kg. It is hunted for its bone and fat. Habitat: It is found in dense forest of Terai region. It is an endangered bird of Nepal. Food: It feeds on insects, fruits and small vertebrates. Life span: Its life span is about 6 to 7 years. Project work Project work Visit a zoological garden (zoo) or any protected area near your locality. Collect information on scientific name, food, habitat, body structure, life span, etc. of the animals found in that place. Prepare a short report and submit to your science teacher. Conservation of endangered species of animals and birds The animals are being listed as endangered due to hunting and smuggling. 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 completely disappear 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.

Oasis School Science and Technology - 10 161 Ways to conserve endangered species 1. Conservation of ecosystem Conservation of ecosystem is very important aspect in the conservation of endangered animals and plants. Animals and birds can live in their natural environment. The habitats for birds and animals are provided by the natural ecosystem. If we want to conserve the rare 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 Some people hunt for pleasure, while others hunt 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 The awareness campaign should be carried out at both the national and local levels. 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 Public participation is very important aspect in conservation. If we want to save endangered animals, we must conduct conservation programs. 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 Every nation requires development, but this does not suggest doing things that are unnecessary in the 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, harmful chemicals, etc. Those things can hugely affect the environment and that deplete the rare birds, animals, and other living beings too. That is why the adverse should be controlled in the time of conducting development activities. 6. Appropriate laws and strict implementation We must develop and strictly enforce appropriate laws at the national and local levels to protect endangered animals and plants. 7. Ex situ conservation Some endangered animals and birds can be saved in exsitu habitats such as aquariums, botanical gardens, zoos, and zoological parks. Some traditionally used medicinal plants Since prehistoric times, medicinal plants have been discovered and used in traditional forms of medicine. Plants produce hundreds of chemical compounds for functions

162 Oasis School Science and Technology - 10 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. Examples are Tulsi, Aloevera, Flagroot, Neem, Yarshagumba etc. Some of them are discussed below: 1. Holy basil (Ocimum tenuiflorum) Holy basil is an aromatic perennial plant. It is also known as tulsi or tulasi. 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. 2. Aloevera (Aloe vera) Aloevera is a type of succulent plant. It 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. 3. Flagroot (Acorus calamus) In Nepali, it is termed to as bojho. 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. 4. Asiatic pennywort (Centela asiatic) It is a herbaceous perennial plant that is used in cooking and as a medicinal herb. 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 varioud disorders and minor wounds. It may have adverse effects on liver function when used for a long period of time. Fig: Holy basil Fig: Aloevera Fig: Flagroot Fig: Asiatic pennywort

Oasis School Science and Technology - 10 163 5. Mugwort (Artemisia vulgaris) In Nepali, it is known as titepati. 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. 6. Heart-leaved moonseed (Tinospora cordifoli) It is also known as gurjo. It has been used in Ayurvedic medicine to treat a variety of diseases. It gets it name by its heart shaoed 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. 7. Malabar Nut (Justicia adhatoda) Malabar is a small evergreen, sub-herbaceous bush that grows in open plains, particularly in the 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. 8. Neem (Azadirachta indica) It is a natural herb obtained from the neem tree. Neem oil is extracted from its fruits and seeds. It is a fast-growing tree. It is deciduous, so many of its leaves fall off during the cold 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. Fig: Mugwort Fig: Heart-leaved moonseed Fig: Malabar Nut Fig: Neem

164 Oasis School Science and Technology - 10 9. Yarsagumba (Cordyceps sinensis) It can be found at high altitudes, primarily in the Himalayan region. Because of its high demand, it is regarded as biological gold. 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 heat diseases, mental diseases etc. 10. Turmeric(Curcuma loga) Termeric can be found throughout Nepal. Its modified stem is present in the soil. It contains the chemical curcumin, which turns it yellow and makes it 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 Plants' natural ecosystems should be protected from forest fires, overgrazing, urbanization, industrialization, road construction and other threats. 2. Increase plantation of endangered species of plants Plant seeds from endangered species should be collected, preserved, and grown in a nursery. They are then planted in suitable habitat to increase their population. If seeds are not available, the tissue culture method can be used to multiply them. 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. 4. Appropriate laws and strict implementation We must develop and strictly enforce appropriate laws at the national and local levels to protect endangered, rare, and medicinal plants. 5. Protection of plants from their extinction Plant species that are endangered should be protected from extinction. If they are extremely rare, we should protect them using both in situ and ex situ conservation methods. Fig: Yarsagumba Fig: Turmeric

Oasis School Science and Technology - 10 165 Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. The natural activities also change the climate. Climate change is a natural process. Human activities are increasing the rate of climate change. However, it also changes naturally. Some natural activities that change climate are: Volcanic eruption: It releases a tremendous amount of heat, carbon dioxide and water vapour into the air. It could cause climate change. Forest fire: Wild forest fire destroys millions of plants each year. Since trees are lost, and smoke is produced, it can harm the climate. 2. Asiatic elephant is an endangered animal. Explain why it is an endangered animal. The Asiatic elephant is an endangered animal. It is classified as an endangered animal because its population has declined by 50% within the last few decades due to loss of habitat, poaching and pollution. 3. List the effect of climate change on human health. Climate change has adverse effects on the environment, animals, plants and humans. Some harmful effects of climate change on human health are listed below: i. Increased probability of cardiovascular diseases. ii. More number of people with respiratory diseases. iii. Spread of infectious disease frequently resulting in a pandemic. iv. Many children are suffering from undernutrition because of a lack of food. v. Increase in mental illness, allergies, injuries and poisoning. 4. How does climate change occur due to industrialization? Industrialization is the process of development of many industries in a country on a wide scale. It has various disadvantages. Climate change is one of them. The industries occupy lots of lands. Forests are lost to make the land for industries. Industries have many machines that run on fossil fuels. If there are more industries more fossil fuel is consumed. It will release more greenhouse gases such as carbon dioxide and water vapour. Solid waste from industries is either dumped or burnt. It also produces greenhouse gases. The mixing of greenhouse gases in the atmosphere is bad for the environment. It traps more solar radiation. It increases the temperature of the earth. It will disturb the water cycle, wind and weather. It will change the climate of a place. 5. Write in brief about the effects of climate change on agriculture. Climate change harms agriculture. Some of them are: i. Regular crops have difficulty growing due to climate change. ii. Crops will be infested with unknown bacteria, viruses and fungi. iii. Number of rodents increases which can destroy crops. iv. Changes in weather patterns can disturb the life cycle of crops. v. Seeds and fruit will be smaller. Agricultural production will decrease. vi. Most crops will die due to drought or heavy rainfall.

166 Oasis School Science and Technology - 10 6. Observe the given diagram and answer the following questions i. Write the name of the medicinal plant shown in the diagram. The medicinal plant shown in the diagram is Heart-leaved moonseed (Tinosporacordifoli). ii. Write its three features. Three features of heart-leaved moonseed are: a. It has unisexual flowers. b. It has a heart-shaped leaf. c. It has reddish fruit iii. Mention its uses. Uses of heart-leaved moonseed are: a. It can treat jaundice. b. It can help with chronic diarrhoea and skin diseases. c. It is used to treat bone fractures and snake bites. 7. How does climate change force 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 the 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. iv. Germs, invasive plants and animals spread from one region to another due to climate change. It can spread epidemics and kill endangered species. 8. 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 medicine is 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.

Oasis School Science and Technology - 10 167 Exercises 1. Choose the best answer from the given alternatives. a. Which one of the following is a cause of climate change? i. afforestation ii. fossil fuel iii. sustainable development iv. hydroelectricity b. Which animal is called Rhinoceros unicornis? i. Royal Bengal tiger ii. Unicorn iii. One horned rhinoceros iv. Red panda c. How long does an Asiatic elephant live? i. 7 years ii. 17 years iii. 70 years iv. 80 years d. Which plant is shown in the diagram? i. neem ii. gurjo iii. ghodtapre iv. beshar e. What is the relation between the caterpillar and the fungus that makes yarsagumba? i. symbiotic ii. parasitic iii. saprophytic iv. omnivore f. What group does gurjo belong to? i. endangered ii. medicinal iii. creepers iv. thorny 2. Define the following terms with required examples. a. Climate change b. Endangered species c. Medicinal plants 3. Answer the following questions in very short. a. How many species of mammals are protected mammals in Nepal? b. Write the scientific names of the Royal Bengal tiger. c. What is the habitat of one horned rhinoceros? d. What is the average mass of an Asiatic rock python? e. Where are red pandas found? f. Write the names of two medicinal plants. g. What is the cause of the rise of sea level? h. Give two examples of endangered species of animal found in Nepal. i. Which part of bhojo is used as medicine? j. Which medicinal plant is used for the treatment of cough and cold? 4. Give reasons. a. Irregular rainfall is common in Nepal nowadays. b. Greenhouse effect and global warming increase the sea level. c. Climate change can cause a decline in the population of endangered species. d. Ashuro and water is used to rinse the mouth. e. Tulsi and neem are lifesaving multiuse medicinal plants. f. Yarsagumba powder is dissolved in milk and used as energetic drinks.

168 Oasis School Science and Technology - 10 g. Biodiversity is declining in Nepal. h. Endangered animals are poached. i. Population of the royal Bengal tiger is increasing in Nepal. j. Hunting wild animals should be prevented. 5. Differentiate between the following. a. Weather and climate change b. greenhouse effect and climate change 6. Answer the following questions in short. a. What human activities are responsible for climate change? b. What changes are observed in the environment due to climate change? c. What can we do to reduce climate change? d. What should the government do to adapt to climate change? e. Write a short note on one-horned rhinoceros. f. Deforestation and industrialization cause climate change. Justify this statement. g. What is neem used for? h. How has climate change disturbed agriculture? i. We should train local people to protect, harvest and process medicinal herbs, so that medicinal herbs can be protected and promoted. Justify. j. Conservation and promotion of medicinal herbs provide economic aid to local people and the country. Discuss. k. What can we do to prevent endangered species from going extinct? 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. 7. Answer the following questions on the basis of the given figure. i. What is the name of the organism shown in the diagram? ii. Where is it found? iii. Mention its uses. 8. Answer the following long questions. a. How does climate change affect our life? Discuss. b. Enlist some protected animals of Nepal. Write a short note on three of them. c. What are medicinal plants? Enlist some medicinal plants and write a short note on any three. d. How does climate change occur due to an increase in the release of greenhouse gases? e. How does climate change occur due to deforestation? Write in brief. f. Write in brief about the impact on human settlement and physical facilities due to climate change. g. Snow does not last long in the mountains of Nepal nowadays. It melts faster and causes floods in the Terai. What is the cause of the faster melting rate of snow from the mountains of Nepal? What can be done to prevent it?

Oasis School Science and Technology - 10 169 Key terms and terminologies 1. Force : Force is a pull or push which changes or tends to change the state of rest or of uniform motion or the shape and size of a body. 2. ISS : ISS means international space station. 3. Non-contact forces : The forces which do not involve physical contact between the objects but act through the space between them are called non-contact forces. 4. Gravitation : Gravitation is the force of attraction which exists between any two bodies due to their masses. 5. Newton's law of gravitation: Newton's law of gravitation states, “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 distance between their centres.” UNIT 7 FORCE AND MOTION Estimated teaching periods Theory 8 Practical 2 • 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 The Sequence of Curriculum Issued by CDC Sir Isaac Newtonis 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. About the Scientist Sir Isaac Newton (1642–1727 AD)

170 Oasis School Science and Technology - 10 6. Gravitational Constant (G): Universal Gravitational Constant (G) is the force of attraction which exists between two bodies of unit masses kept at a unit distance from their centres. 7. Gravity : Gravity is the force that pulls a body towards the centre of the earth or a planet. 8. Gravitational field : The gravitational field of a planet is the area around the planet up to where the gravity of the planet has its influence on an object. 9. Acceleration due to gravity: The acceleration produced in a freely falling body due to the influence of gravity is called acceleration due to gravity. 10. Mass : The total quantity of matter contained in a body is called its mass. 11. Weight : The weight of a body is defined as the force with which it is pulled towards the centre of the earth or a planet. 12. Free fall : When a body is falling only under the effect of gravity without external resistance, the fall of the body is called a free fall. 13. Weightlessness : When a body is in a state of zero weight, it is called weightlessness. Introduction We use force to do many things in our everyday lives. Pull, push, squeeze, stretch, etc. denote a force. We can push or pull things with our hands. A force can change the position and shape of a body. Similarly, a force can change the direction of motion and speed of a moving body. However, if a force is applied to move a tree or a fixed wall, the effort will not be effective. Hence, force is a pull or push which changes or tends to change the state of rest or of uniform motion or the shape and size of a body. In the SI system, force is measured in newton (N) and in the CGS system, it is measured in dyne. There are various types of forces, like the force of friction, the force of gravity, the force of electricity, the force of magnetism, etc. On the basis of physical proximity, forces can be classified into two types: contact force and non-contact force. Reasonable Fact An astronauts in ISS or in the satellite fell weightless. An astronauts in the ISS(international space station) or in the satellite move with the high velocity without any external resistance (free fall). So, they feel weightless. Contact forces are those which act only in physical contact with each other. For example, frictional force, collision force, pull, push, etc. Similarly, the forces which do not involve physical contact between the objects but act through the space between them are called non-contact forces. For example, gravitational force, electrostatic force, magnetic force, etc. These forces come into action even though the objects are not in physical contact. The Fact File 1 N= 105 dyne

Oasis School Science and Technology - 10 171 magnitude of non-contact force like like gravitational force depends on their masses and the distance of separation. This force increases with the increase in their masses and decreases with the increase in distance. Gravitation If a stone is raised above the ground and released, it falls towards the earth. Since the stone starts moving downwards, a force must be acting on it. The force is attributed to the attraction between the earth and the stone. It is called the force of gravity. Gravitation is the force of attraction which exists between any two bodies due to their masses. In fact, the earth attracts all the objects towards its centre. It is due to the gravitational force of the earth that all objects fall towards the earth when released from a certain height. The gravitational force of the earth pulls every object towards its centre. Therefore, we should apply a force to lift a body from the earth's surface. It was Newton who said that every object in this universe attracts every other object with a force called the gravitational force. Gravitation between small bodies is less and between bigger bodies is more For a small body, the force of gravitation is small and cannot be detected easily. Newton concluded that it is not only the earth which attracts the other objects but every object in this universe attracts every other object. For example, two stones lying on the ground attract each other. The force of gravitation between them is very small and we do not notice any motion. However, if one of the bodies has a very large mass (like the earth), the small body lying near it moves towards the bigger body. Gravitational force is responsible for the existence of the solar system Since the masses of the sun and the earth are very large, they exert a very large force on one another. The mass of sun is so large that even the sum of the masses of all its planets and satellites is only about 0.0015th part of the sun. It is the gravitational force between the sun and the earth which keeps the earth in uniform circular motion around the sun. Similarly, the gravitational force between the earth and the moon makes the moon revolve at uniform speed around the earth. Thus the gravitational force is responsible for the existence of the solar system. Gravitational force is more in liquids The effect of gravitation can be observed more on liquids than on solids. The tides in the sea are due to the force of attraction, which the sun and the moon exert on the water surface in the sea. Approximately twice a month at the time of the new moon and full moon, the tide range reaches its maximum due to the effect of the combined gravitational Fact File 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 them. Fact File Gravitational force between two bodies is same all over the universe, either they are on the earth or on the Jupiter. Fact File 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.

172 Oasis School Science and Technology - 10 force of the sun and the moon on the earth when they lie on a straight line. Sun F F Earth Moon Fig. 7.1. Gravitational force Thus, gravitation is the force of attraction, which exists between any two bodies of the universe due to their masses. Newton was the first person who gave the popular law in 1687 AD called Newton’s universal law of gravitation. Reasonable Fact The effect of gravitational pull of the sun and moon is more in liquids on the earth. 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. Newton's law of gravitation states, “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 distance between their centres.” Let us consider two bodies of masses 'm1 ' and 'm2 ' separated by a distance 'd' from their centres. If the force of attraction between them is F, F d m1 m2 Fig.7.2 According to Newton’s law of gravitation, i. The gravitational force between two bodies is directly proportional to the product of their masses, i.e., F ∝ m1 × m2............................. (i) ii. The gravitational force between two bodies is inversely proportional to the square of the distance between their centres, i.e.,

Oasis School Science and Technology - 10 173 F ∝ 1 d2 .............................. (ii) Combining (i) and (ii), we get F ∝ m1 m2 d2 ∴ F = G m1 m2 d2 [Where 'G' is a constant called the universal gravitational constant. Its value is 6.67×10-11 Nm2 /kg2 .] Reasonable Fact Newton's law of gravitation called the universal law. Newton's law of gravitation holds true or is applicable to all the objects present in the universe, whether the objects are terrestrial or celestial. The gravitational force between any two objects exists everywhere in this universe. Therefore, Newton's law of gravitation is also called the universal law of gravitation. Major Consequences of Gravitational Force i. Existence of solar system, galaxy and constellations ii. Revolution of planets around the sun iii. Revolution of natural satellites around the planets iv. Formation of tides in the sea v. Rainfall on the earth Applications of Newton’s Law of Gravitation i. This law helps us to determine the mass of the earth and other heavenly bodies. ii. This law helps us to calculate the distance between any two heavenly bodies such as the earth and moon, sun and earth, etc. iii. This law helps in discovering new planets, stars and other heavenly bodies. Universal Gravitational Constant (G) Universal Gravitational Constant (G) is the force of attraction which exists between two bodies of unit masses kept at a unit distance from their centres. 'G' is a scalar quantity. Its value remains the same throughout the universe and is independent of the nature and size of the bodies as well as the nature of the medium between them. According to Newton's law of gravitation, we have F = G Mm d2 If, M = m = 1kg and d = 1m, then F = G 1×1 12 ∴ F = G Fig. 7.3 F = G 1m 1 kg 1 kg

174 Oasis School Science and Technology - 10 Thus, universal gravitational constant is the force of attraction between two bodies each of 1 kg mass separated at 1 m apart from their centres. SI Unit of G According to Newton's law of gravitation, the gravitational force acting between any two bodies is given by F = G Mm d2 This formula can be rearranged to get the expression for G as follows: or, G = = = Fd Mm Nm kg kg Nm kg 2 2 2 2 . / ∴ The SI unit of gravitational constant (G) is Nm2 /kg2 or Nm2 kg-2. Variation of Gravitation with Mass and Distance A. When the mass of a body is doubled keeping the distance between two bodies constant According to Newton's law of gravitation, F GMm d When themass of a body isdoubled M M Then F G M m d new = → = = 2 2 2 2 , , ( ) 2 2 2 2 GMm d F F GMm d       = =       Q Hence, the gravitation between two masses is doubled when the mass of a body is doubled keeping the distance between them constant. Activity 1 Visit website Phet interactive simulation and test variation of gravitation with mass and distance. https://phet.colorado.edu/sims/html/gravity-force-lab/latest/gravity-force-lab_en.htm Fact File The value of gravitational constant (G) is 6.67×10-11 Nm2 / kg2 . It was calculated by Henry Cavendish by using a sensitive balance called the torsion balance in 1798 AD. Fact File If 'G' by some miracle were suddenly multiplied by a factor of 10, we would be crushed to the floor by the earth's attraction and if 'G' were divided by this factor, the earth's attraction would be so weak that we would be able to jump over a building easily. Fig. 7.4(a) Fig. 7.4(b) d M m F = G Mm d2 d 2M m Fnew = G (2M).m d2

Oasis School Science and Technology - 10 175 B. When the distance between two bodies is halved keeping the masses constant According to Newton's law of gravitation, F GMm d When themass of a body isdoubled M M Then F G M m d new = → = = 2 2 2 2 , , ( ) 2 2 2 2 GMm d F F GMm d       = =       Q When the distance between two bodies is halved, d d Then F G Mm d G Mm d GMm d F F GMm d new → = ( ) = =       = =      2 2 4 4 4 2 2 2 2 , Q  Hence, the gravitation between two masses becomes four times the previous force when the distance between them is halved keeping their masses constant. Worked out Numerical 1 Calculate the gravitational force between two masses of 30 kg and 10 kg when they are kept 500 cm apart. Solution: Given, Mass of one body (m1 ) = 30 kg Mass of another body (m2 ) = 10 kg Distance (d) = 500 cm = 500 100 = 5 m [ ∵ 1 m = 100cm] Gravitational force (F) = ? We have, F = G m m d 1 2 2 = 6 67 10 30 10 5 11 2 . ( ) × × × − [ ∵ G = 6.67 × 10-11 Nm2 /kg2 ] = 8 × 10-10 N. ∴ The gravitational force existing between them is 8 × 10-10 N. Fig 7.5(a) Fig. 7.5 (b) d M M m m F = G Mm d2 d 2 Fnew = GMm ( d 2 ) 2

176 Oasis School Science and Technology - 10 Reasonable Fact There is a mutual force of attraction between two buildings on a city but they do not move toward each other. According to Newton's universal law of gravitation, there is a mutual force of attraction between two building on a city 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. Worked out Numerical 2 Calculate the gravitational force acting on a body of mass 50 kg on the surface of the earth. The mass and radius of the earth are 6×1024 kg and 6400 km respectively. Solution: Given, Mass of the earth (M) = 6 × 10 24 kg Mass of a body (m) = 50 kg Radius of the earth (R) = (d)= 6400 km = 6400 × 1000m [ ∵ 1km = 1000 m] Gravitational force (F) = ? We have, F = G Mm d2 = 6 67 10 6 10 50 6400 1000 11 24 2 . ( ) × × × × × − ( ∵ G = 6.67 × 10-11 Nm2 /kg2 ) = 488.5N ∴ The gravitational force between them is 488.5N. Activity 2 Go to an open ground. Take a ball and throw it upward. What do you observe? It reaches a certain height and then it starts falling. What is the reason behind it? Gravity All bodies close to the earth's surface are attracted to it. When a ball is dropped from a roof of a house, it falls on the surface of the earth. Similarly, fruits fall from a tree. The force that pulls these objects downwards is the gravity of the earth. Thus, gravity is the force that pulls a body towards the centre of the earth or a planet. 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 centre. Fig. 7.6

Oasis School Science and Technology - 10 177 Gravitational Field All the bodies present inside the gravitational field of the earth or a planet are pulled towards the centre of the earth or the planet. The gravitational field of a planet is the area around the planet up to where the gravity of the planet has its influence on an object. The gravitational field of a planet depends on the mass and radius of the planet. The force of attraction between a planet and a body on the surface or near its surface is called gravity, or weight of the body on that planet. So 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 Effect of gravity is more for big object Different heavenly bodies have their own gravity. The effect of the earth's gravity is more on a body of larger mass than that on a body of a smaller mass. Therefore, it becomes difficult to lift a large stone than a smaller one. The weight of a body is the measure of the gravity acting on the body. Worked out Numerical 3 Calculate the weight of a body of mass 50 kg: (i) on the surface of the earth and (ii) on the surface of the moon. [Given, mass of the earth = 6×1024 kg, mass of the moon = 7.2 ×1022 kg, radius of the earth = 6400 km, radius of the moon = 1.7× 10³ km] Solution: Given i. On the surface of the earth, Mass of the earth (M) = 6 × 1024 kg Mass of the body (m) = 50 kg Radius of the earth (R) = 6400 km = 6400 × 1000 m Weight of the body (F or W) = ? We have, F = W = GMm R2 Fact File The moon has its own gravity like that of the earth and other heavenly bodies. According to scientists, the gravity of the earth is about six times more than that of the moon. Thus, a body weighing 100 N on the moon weighs 600 N on the earth. ∴ F = W = GMm R2

178 Oasis School Science and Technology - 10 = 6 67 10 6 10 50 6400 1000 11 24 2 . ( ) × × × × × − [ ∵ G = 6.67 × 10-11 Nm2 /kg2 ] = 488.5 N ∴ Weight of a body on the earth's surface = 488.5 N. ii. On the surface of the moon, Given, Mass of the moon (M) = 7.2 × 1022 kg Mass of the body (m) = 50 kg Radius of the moon (R) = 1.7 ×10³ km = 1.7 × 10³ ×1000 m = 1.7 × 106 m Weight of the body (F or W) = ? We have, F = W = GMm R2 = 6 67 10 7 2 10 50 1 7 10 11 22 6 2 . . ( . ) × × × × × − [ ∵ G = 6.67 × 10-11Nm2 /kg2 ] = 83.08 N ∴ Weight of the body on the surface of the moon = 83.08 N Now, compare the weight of a body of mass 50kg on the surface of the earth and that on the surface of the moon. You notice that the weight of the same body differs on the surface of the earth and on the moon. It also proves that the weight of a body on the surface of the moon is about 1 6 th of that on the surface of the earth. Effects of Gravity The gravity of the earth affects various activities and objects on the earth. The major effects of the earth's gravity are given below: i. Falling of objects towards the centre of the earth ii. Stability of large buildings and bridges iii. Existence of the atmosphere on the surface of the earth iv. Flowing of rivers v. Blowing of wind Fact File An astronaut needs 92 minutes to revolve round the earth from ISS.

Oasis School Science and Technology - 10 179 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. Acceleration due to Gravity When a body is dropped from a certain height, its velocity increases at a constant rate. It means that a uniform acceleration is produced in the falling body due to the gravitational pull of the earth. Thus, the acceleration produced in a freely falling body due to the influence of gravity is called acceleration due to gravity. It is denoted by 'g'. The SI unit of acceleration due to gravity is meter per second per second (m/s2 ). From the above figure, it becomes clear that the acceleration produced in freely falling bodies will be the same, and it does not depend on the mass of the falling bodies in the absence of external resistance. Gravity and acceleration due to gravity are two different physical quantities. The acceleration produced in the bodies falling towards the surface of the earth is the effect of earth's gravity. Reasonable Fact Aristotle believed that heavier objects accelerate more and fall faster than lighter ones. Galileo Galilei experimented at the leaning tower of Pisa where he dropped two spheres of the same volume but different masses. He discovered that both spheres had the same acceleration and reached the ground at the same time. Relation between Acceleration due to gravity and Radius of the earth Let's consider a body of mass 'm' is falling on the surface of the earth of mass 'M' and radius 'R'. Then the force exerted by the earth on the body is given by Newton’s law of gravitation, i.e. F = GMm R2 ..............................(i) The force exerted by the falling body is given by F = mg ________ (ii) (Where 'g' is the acceleration produced in the falling body) Same acceleration is produced in all the falling bodies in the absence of external resistance Vacuum Fig. 7.7 Fig. 7.8 R M Earth m

180 Oasis School Science and Technology - 10 From (i) and (ii), we get mg = GMm R2 or, g = GM R2 or, g ∝ 1 R2 [Where G and M are constants.] ∴ g ∝ 1 R2 is proved. Thus, acceleration (g) produced on the surface of the earth is inversely proportional to the square (R) of the radius of the earth. So, when 'R' decreases, 'g' increases and when 'R' increases 'g' decreases in squared value. Variation of acceleration due to gravity on the earth surface From the relation g = GM R² , it is clear that the value of acceleration due to gravity (g) depends on the values of M, R and G. Since 'M' and 'G' are always constant, the value of 'g' remains constant as long as the radius of the earth 'R' remains constant. Therefore, the value of 'g' remains constant at a given place on the surface of the earth. However, the value of 'g' does not remain constant at all places on the surface of the earth. The earth is not a perfect sphere. It is flat at the poles and bulging at the equator. Similarly, there are high mountains, hills, valleys and plains on the surface of the earth. So the value of 'R' differs from place to place on the surface of the earth. Therefore, the value of 'g' also changes from place to place on the surface of the earth [ ∵ g ∝ 1 R² ]. Since the radius (R) of the earth at the poles is minimum, the value of acceleration due to gravity (g) is maximum, i.e. 9.83 m/s2 . Similarly, the radius (R) of the earth at the equators is maximum, so the value of 'g' is minimum, i.e., 9.78 m/s2 . However, the average value of 'g' on the earth's surface is taken as 9.8 m/s2 . The velocity of the falling bodies When a body falls towards the earth's surface only under the action of gravity, its velocity increases at a constant rate of 9.8 m/s for every second of time it is falling. When a body is dropped freely, it falls with an acceleration of 9.8 m/s2 . Fact File The value of 'g' vary from place to place on the surface of the earth. The value 'g' is inversely proportional to the square of the radius of the earth. The earth is not perfectly spherical. It is flat at the poles and bulges at the equator. Similarly there are plains, hills, valleys and mountains of various heights on the surface of the earth. Due to this, the distance between the center and various places of the earth is variable. Therefore, the value of 'g' varies from place to place on the surface of the earth. R more R less R g ∝ 1 R² Earth Pole (g=9.83 m/s2 ) Equator (g=9.78 m/s2 ) Fig. 7.9 Fig. 7.10 Earth m M g = 9.8 m/s²

Oasis School Science and Technology - 10 181 When a body is thrown vertically upwards, it undergoes a retardation of 9.8 m/s2 . So the velocity of a body thrown upwards will decrease at the rate of 9.8 m/s in every second of time and the velocity decreases until it reaches zero. The body falls back to the earth with an acceleration of 9.8 m/s2 . 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. Prove that the acceleration produced on a freely falling body is independent of the mass of that body. Let's consider a body of mass 'm' is falling freely towards the surface of the earth. Let the mass and radius of the earth be 'M' and 'R' respectively. According to Newton’s law of gravitation, F = GMm R2 ............................. (i) From Newton's second law of motion, F = mg............................. (ii) From (i) and (ii), we have mg = GMm R2 or, g = In the above expression, the mass of the falling body is cancelled, and there is no mass of the falling body. So, the acceleration produced on a freely falling body is independent of the mass of that body. M Earth R m Fig. 7.11 GM R2 Fact File All freely falling bodies, small or large, fall together on the surface of the earth under the same effect of acceleration due to gravity (g).

182 Oasis School Science and Technology - 10 Worked out Numerical 4 Calculate the value of acceleration due to gravity on the surface of the earth. The mass and radius of the earth are 6 × 1024 kg and 6380 km respectively. Solution: Given, Mass of the earth (M) = 6 × 1024 kg Radius of the earth (R) = 6380 km = 6380 × 1000 m Acceleration due to gravity (g) = ? We have, g = GM R2 = 6 67 10 6 10 6380 1000 11 24 2 . ( ) × × × × − [ ∵ G = 6.67 × 10–11 Nm2 /kg2 ] = 9.8 m/s2 Acceleration due to gravity at a certain height (h) from the earth's surface Let us consider a body of mass 'm' is placed at a height 'h' above the surface of the earth of mass 'M' and radius 'R' as shown in the figure. According to Newton's law of gravitation, F GMm R h or GMm R h or g GM R h = + = + = + ( ) mg' ( ) ' ( ) 2 2 2 ∴ g' = GM (R + h)2 This formula proves that acceleration due to gravity (g) decreases as the height from the surface of the earth increases. Worked out Numerical 5 The mass of the earth is 6×1024 kg and its radius is 6400 km. Calculate the acceleration due to gravity at the top of Mt. Everest of height 8848 m from the earth's surface. Also, calculate the weight of a person of mass 60 kg on top of Mt. Everest. Solution: Given, Mass of the earth (M) = 6×1024 kg Radius of the earth (R) = 6400 km = 6400×1000 m = 6.4 ×106 m Height of Mt. Everest (h) = 8848 m R h Earth m Fig. 7.12 Fact File Since the distance from the center of the earth to a certain height (R+h) is greater than that on the surface, the value of g' is less at the given height than that on the surface of the earth. Similarly, the value of 'g' is less at the top of a hill than at its foot. [∵ F = mg' g' = acceleration due to gravity at the given height]

Oasis School Science and Technology - 10 183 Acceleration due to gravity (g') = ? According to the formula, g' = F GMm R h or GMm R h or g GM R h = + = + = + ( ) mg' ( ) ' ( ) 2 2 2 = 6.67 × 10–11 × 6 × 1024 (6.4 × 106 + 8848)² = 4.002 × 1014 4.1 × 1013 = 9.76 m/s2 ∴ The acceleration due to gravity at the top of Mt. Everest is 9.76 m/s2 . Now, Acceleration due to the gravity (g') = 9.76 m/s² Mass of the person (m) = 60 kg Weight of the person (W) = ? According to the formula, W = m × g' = 60 × 9.76 = 585.6N ∴ Weight of the person on the top of Mt. Everest = 585.6 N. Reasonable Fact The objects fall faster at the pole than at the equator. 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. Differences between Acceleration due to gravity (g) and Gravitational constant (G) S.N. Acceleration due to gravity (g) S.N. Gravitational constant (G) 1. The acceleration produced on a freely falling body under the effect of gravity is called acceleration due to gravity. 1. Gravitational constant is the force of attraction between two bodies of unit mass each kept at unit distance apart from their centres. 2. It is a variable quantity. Its value changes from place to place. 2. It is a constant quantity. 3. It is a vector quantity. 3. It is a scalar quantity. 4. Its SI unit is m/s2 . 4. Its SI unit is Nm2 /kg2 .

184 Oasis School Science and Technology - 10 Differences between Acceleration due to gravity (g) and Gravity (F) S.N. Acceleration due to gravity (g) S.N. Gravity (W or F) 1. The acceleration produced on a freely falling body under the effect of gravity is called acceleration due to gravity. 1. Gravity is the force by which a body is attracted towards the centre of the earth or any other heavenly body. 2. Its SI unit is m/s2 . 2. Its SI unit is N. 3. It is the effect of gravity. 3. It is the cause of acceleration due to gravity. Coin and Feather Experiment On the basis of his experiments, Galileo Galilei concluded that the acceleration of an object falling freely towards the earth does not depend on the mass of the body. To verify this fact, Robert Boyle performed an experiment in a vacuum. This is a famous experiment to prove that the acceleration produced on every freely falling body remains the same. It does not depend on the mass of the falling body. In this experiment, a coin and a feather are kept inside a tall glass tube and its ends are closed. The tube is inverted as soon as possible. The coin reaches the bottom earlier as compared to the feather as the tube contains air. Then the tube is made free from air by using a vacuum pump. When the tube is quickly inverted, the coin and the feather reach the bottom simultaneously. When the tube contains air, the feather falls slower than the coin. Because the resistance offered by air on the feather is more as the surface area of the feather is larger than that of the coin. Conclusion of feather and coin experiment The acceleration produced on freely falling bodies remains the same for all the bodies and it is independent of the mass of those bodies. Activity 3 Take a sheet of paper and a stone. Drop them simultaneously from the top of a building. Observe whether both of them reach the ground simultaneously or not. When a body falls down, air offers resistance to the falling body due to friction between the body and air. The resistance offered by air to the paper is more than that to the Coin Air Vacuum Feather Fig. 7.13 Coin and feather experiment Fact File An astronaut uses space capsule connected with a parachute while returning to the earth. Due to air resistance, the parachute falls with a constant velocity and astronaut remains safe.

Oasis School Science and Technology - 10 185 stone. If this experiment is conducted in a vacuum, the paper and the stone would fall simultaneously. Activity 4 Take two stones of different sizes. Put a sheet of tin on the ground and drop these stones from the same height simultaneously on the tin. Listen to the sound produced on their falling. Observe whether they fall simultaneously or not. What is the reason behind it? Activity 5 Take two sheets of paper (one folded and another unfolded) instead of the above two stones and repeat the activity 3. What do you observe? When a parachutist jumps from a very high altitude, s/he does not get hurt. It is because the resistance offered by the air, reduces acceleration to zero. Parachute falls with uniform velocity due to air resistance. It is not a freefall. Activity 6 Take a thick plastic sheet. Cut it in the form of a circle of radius 20 cm. Make 8 holes at the edge of the plastic. Tie a stone with the support of the thread through these holes. Drop it from the top of a building and observe the motion of the model of parachute. Write down the conclusion of this activity. Fig.7.14 (b) Model of a parachute Plastic Thread Stone Worked out Numerical 6 A person can lift 50 kg mass on the earth’s surface. Find the mass that he can lift on the surface of the moon. The value of 'g' on the moon is 1.66m/s². Solution: Let 'm' be the mass that the person can lift on the surface of the moon. Now, Force applied by the person on the earth’s surface = Force applied by the person on the surface of the moon or, mearth × gearth = m × gmoon or, 50 × 9.8 = m × 1.66 or, 50 9 8 1 66 × . . = m m = 295.18 kg Thus, the person can lift 295.18 kg on the surface of the moon. Fig.7.14 (a) Paragliding

186 Oasis School Science and Technology - 10 Mass The total quantity of matter contained in a body is called its mass. It is a constant quantity. The mass of a body remains the same wherever it be on the earth, moon or even in outer space. It is measured by a pan balance or a beam balance. It is a scalar quantity. The mass of a body cannot be zero. It is measured in kilogram (kg), gram (g), milligram (mg), etc. Mass of a body depends on: i. size of atoms or molecules and ii. number of atoms or molecules of the body. Weight Weight of a body is the gravity acting on the body. Thus, the weight of a body is defined as the force with which it is pulled towards the centre of the earth or a planet. It is a variable quantity. It has direction as well as magnitude. The direction of the weight is towards the centre of a massive body (like the earth). So, weight is called a vector quantity. It is measured by using the spring balance. The SI unit of weight is newton (N). The weight of a body at a place depends on : i. mass of the body, and ii. value of acceleration due to gravity at that place. Variation in weight of a body The weight of a body is directly proportional to the mass of that body. The weight of a body is calculated by W = m×g. The value of g (acceleration due to gravity) differs from place to place. Therefore, the weight of a body also differs from place to place. The weight of a body becomes zero where g = 0, such as in interplanetary space. In such places we feel true weightlessness. We know that acceleration due to gravity of the moon is six times less than that of the earth. So, the weight of a body on the moon will be about one-sixth of its weight on the earth. Fact File Weight of a body is found less at the top of a mountain than at the bottom of it. The value of 'g' is more at the bottom of a mountain due to less radius and less at the top of the mountain due to more radius (∵ g ∝ 1 R2). Therefore, the weight of an object is less at the top of a mountain than at the bottom of the mountain. Fact File The weight of an object is more at the polar region than that in the equatorial region of the earth. The value of 'g' is more at the poles (i.e. 9.83 m/s2 ) due to less radius and less at the equator (i.e. 9.78m/s2 ) due to more radius (∵ g ∝ 1 R2). Therefore, the weight of an object is more at the polar region than in the equatorial region of the earth. Fact File In Nepal, weight (W) as well as acceleration due to gravity(g) is maximum in Kechana kawal (Jhapa).

Oasis School Science and Technology - 10 187 Differences between Mass and Weight S.N. Mass S.N. Weight 1. The total quantity of matter present in a body is called its mass. 1. The weight of a body is the measure of the gravity acting on the body. 2. Its SI unit is kg. 2. Its SI unit is N. 3. It is measured by using a beam balance. 3 It is measured by using a spring balance. 4. It is a scalar quantity. 4. It is a vector quantity. 5. It is a constant quantity for a particular body. 5. It is a variable quantity. Reasonable Fact A person who can lift 50 kg on the earth can lift approximately 300 kg on the moon. 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. Worked out Numerical 7 The radius of Jupiter is 11 times more than that of the earth and the mass of Jupiter is 319 times more than that of the earth. Now, find out how many times more the gravity of Jupiter is than that of the earth. Solution: Given, Mass of the earth = me Mass of Jupiter (mj ) = 319 × me Radius of the earth = re Radius of Jupiter (rj ) = 11 × re Let the mass of a body be 'm'. Gravity acting on a body on the surface of Jupiter (F) Hence, the gravity of Jupiter is about 2.6 times more than that of the earth. = = = = G m m r G m m r G m m r G m m r j j e e e e e e 2 2 319 11 319 121 2 6 ( ) ² . ²

188 Oasis School Science and Technology - 10 Equations of Motion for Freely Falling Bodies Freely falling bodies fall with uniform acceleration (g) towards the surface of the earth or a planet. The three modified equations of motion can be applied to the motion of freely falling bodies, which are as follows: i. v = u + gt ii. h = ut + 1 2 gt2 iii. v2 = u2 +2gh These modified equations of motion are used to solve numerical problems related to freely falling bodies. We should remember the following points for the motion of freely falling bodies: i. When a body is falling vertically downwards, the acceleration due to gravity (g) is taken to be positive. ii. When a body is thrown vertically upwards, the acceleration due to gravity (g) is taken to be negative. iii. When a body is dropped freely from a height (h), its initial velocity (u) becomes zero. iv. When a body is thrown vertically upwards, its final velocity (v) becomes zero. v. The time taken by a body to rise to the highest point is equal to the time it takes to fall from the same height. 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 Worked out Numerical 8 To estimate the height of a bridge over the Mahakali River, a stone is dropped freely in the river from the bridge. The stone takes 2 seconds to touch the water surface in the river. Calculate the height of the bridge from the water level. (g = 9.8m/s2 ) Solution: Given, Initial velocity (u) = 0 m/s [∵ The stone is dropped freely.] Time taken (t) = 2 s Acceleration due to gravity (g) = 9.8 m/s2 Height of the bridge (h) = ? Where, v = final velocity u = initial velocity g = acceleration due to gravity t = time taken h = height from the earth's surface

Oasis School Science and Technology - 10 189 According to the formula, h = ut + 1 2 gt2 = 0 × 2 + 1 2 × 9.8 × 22 = 1 2 × 9.8 × 4 = 19.6 m ∴ The height of the bridge above the water level is 19.6 m. Worked out Numerical 9 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 Free Fall When a body is falling due to the effect of gravity, acceleration is produced in it, which is called acceleration due to gravity. So, if a body is falling only under the effect of gravity, the fall of the body is called a free fall. 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. Conditions for free fall i. The object must be falling under the influence of gravity. ii. There must be no resistance or other forces acting upon the object, such as air resistance or pulling or pushing forces. iii. The object must not be attached to any other object, such as a rope. Some examples of free fall 1. Dropping an object: When we drop an object from a height, it falls under the influence of gravity and experiences free fall. 2. Skydiving: Skydivers jump from airplanes and experience free fall until they deploy their parachute. 3. Bungee jumping: Similar to skydiving, bungee jumpers experience free fall until the bungee cord stops their descent. 4. Astronauts: Astronauts in space are in a constant state of free fall around the Earth, experiencing the feeling of weightlessness. Fact File There is no true freefall on earth because the upthrust of air and friction with air acts on the objects.

190 Oasis School Science and Technology - 10 Activity 7 Take a piece of paper and cut it as a circle of diameter 12 to 16 cm. Draw two perpendicular diameters on the paper. Punch hole at each end of both diameters. Tie an 8-inch long thread on each hole. Tie another end of every thread together and put a weight (eraser or stone or wood). Drop the parachute from a tall place and observe. Make a hole of 1-inch diameter in the middle of the parachute and drop again. Observe. Did you find any difference when the parachute falls? Fact File A man-made satellite can revolve on its own path due to the balance between the force of gravitation and the outward force due to the velocity of the satellite. Centripetal force is required to move a body in a circular path. The direction of this force is towards the center of the circular path. Reasonable Fact The fall of a parachute towards the earth's surface is not a free fall. The fall of an object towards the earth's surface only under the influence of gravity without external resistance is called a free fall. But there is the presence of atmosphere around the surface of the earth, which creates external resistance. Therefore, the fall of a parachute the towards earth's surface is not a free fall. Effect of air resistance on a falling body Activity 8 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. The rate of a falling body is affected by air resistance. The sheet of paper has more resistance to air than the paper ball. Because of this, the piece of paper drops slowly. But the TT ball and paper ball hit the floor at the same time when there isn't much air resistance. The parachute can safely land on the ground because air resistance slows it down. Because of this, the parachute falls at a constant rate without accelerating. About the same thing happens when hail stones fall, hairy seeds disperse, and so on. Fact File Some seeds have fur or feathery parts. They use it to travel farther from thier habitat. The fur acts like a small parachute. It help them to disperse even in weak winds. The upthurst of air and air resistance keep them floating in air.

Oasis School Science and Technology - 10 191 Reasonable Fact Parachutists are not hurt when they jump out of a plane from a very high place. A parachute opens and expands when a parachutist jumps out of a plane. The larger the area of the parachute, the more will be the resistance of the air. So, the acceleration of the parachute decreases. Due to decreased acceleration caused by gravity, a parachutist falls with uniform velocity and zero acceleration. As a result, a parachutists can balance his body and is not hurt when he jumps out of a plane. Activity 9 Take a spring balance, hold it by one hand and measure the weight of a stone. Now release the spring balance along with the stone and note down the reading of the pointer of the spring balance. The value of the weight at the time of the free fall will be zero. Stone weighs 0 Zero Spring balance released Stone weighs Spring balance Spring balance held by hand 5 N 5 N Fig. 7.16 Weight of a body at the time of the free fall Weightlessness The weight of a body on the earth’s surface is the force by which the earth attracts it. The weight of a body is measured by using a weighing machine or a spring balance. Suppose a weighing machine is placed on the floor of a lift parked at the top floor of a tall building, and a man is standing on it. In this condition, the machine shows a certain weight of the man. If the lift is allowed to fall freely, both the weighing machine and the man would fall freely towards the earth with the same acceleration due to gravity. Under this condition, it is not possible to get the value of the weight on the machine. It is to be noted that the weight of the body shown by the machine is due to its reaction force. When the reaction force is zero (at the time of the free fall), the machine shows zero weight. Hence, we can say a man is weightless in a freely falling lift. Thus, a body is said to be weightless when it is falling freely only under the influence of gravity. When a body is in a state of zero weight, it is called weightlessness. It can also be defined as the condition at which a body of a certain mass becomes weightless. Weightlessness in Space An astronaut floats in space when s/he is in a spaceship orbiting the earth. Consider an astronaut in a spaceship orbiting the earth about 1000 km above its surface where the Fig. 7.17 A man falling freely from a lift

192 Oasis School Science and Technology - 10 acceleration due to the gravity of the earth is quite strong, i.e., 7.34 m/s². The weight of the astronaut in the spaceship cannot be zero since the weight = m.g and g cannot be zero. But we can say that the astronaut is weightless. 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. So the astronaut does not exert any force on the sides of the spaceship and appears to be floating weightlessly. Thus, the astronaut feels weightlessness due to the zero reaction force. But true weightlessness is experienced in the region of outer space where the acceleration due to gravity is zero. Reasonable Fact A satellite does not need any energy to revolve around the earth. A satellite does not need any energy to revolve around the earth because of the balanced centripetal and centrifugal forces provided by the gravitational force. 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. Conditions for Weightlessness i. When a body is falling freely (∵ The reaction force is zero during the free fall.) ii. When a body is in space at null point (∵ The value of g = 0, weight = m.g. = m.0 = 0.) iii. When a body is in a rocket which is orbiting around a heavenly body (∵ The body inside the rocket is in a state of free fall.) iv. When a body is at the centre of a planet (∵ g = 0) 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. Fig. 7.18 An astronaut falling freely

Oasis School Science and Technology - 10 193 Reasonable Thinking Skill Reasonable Thinking Skill R T S 1. 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. 2. A satellite does not need fuel to revolve around the earth. A satellite does not need fuel to revolve around the earth because it is in a state of continuous freefall. It uses the earth’s gravitational force as a centripetal force to keep moving around in the orbit. 3. If the earth is compressed to the size of the moon what would happen to the acceleration due to the gravity of the earth? If the earth is compressed to the size of the moon, the mass of the 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 the moon = 1.74 ×106 m Acceleration due to gravity =? Using formula, g = GM R2 = 6.67 × 10–11 × 6 × 1024 (1.74 × 106 )2 = 40.02 × 10–11 + 24 3.0276 × 1012 = 40.02 × 10 -11+243.0276 × 1012 = 13.218 × 10-11 + 24-12 = 13.218 × 10 = 132.1 m/s2 . 4. An object that falls from a significant height can cause more damage than an object that falls from a lesser height. A falling object accelerates due to gravitational pull. When an object falls from a significant height it will have more time to accelerate. So, it gains more momentum. Upon collision with the ground it can have more damage. But if an object falls from a lesser height, it will have less time for acceleration hence it can have less momentum and less damage. 5. Let’s suppose two identical balls A and B are dropped from the same height at the same time. Ball A at the pole and ball B at the equator. Which one will reach the ground faster? Which one hits the ground with more force? If two identical balls A and B are dropped from the same height at the same time, ball A at the pole and ball B at the equator. Ball A dropped at the pole will reach the ground faster than ball B dropped at the equator. It is because the value of acceleration due to gravity is more at the poles than at the equator.

194 Oasis School Science and Technology - 10 At the poles, the earth has a shorter radius than the equator. Acceleration due to gravity is inversely proportional to the radius (g ∝ 1 R2). So, the value of g is more at the poles than at the equator. Due to more value of g, the weight of an object will be more at the poles than at the equator (W = mg). So, ball A dropped at poles will have more weight and hit the ground with more force than ball B. 6. A squeezed paper falls faster than a flat paper if dropped from the same height on the earth. A squeezed paper falls faster than flat paper if dropped from the same height in the earth because the squeezed paper has a small total surface area so it experiences less air resistance. However, flat paper has more total surface area, so it experiences more air resistance. 7. 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. 8. A person thought buying apples in mountains and selling them in Terai using digital balance, will it be profit. Buying apples in mountains and selling them in Terai using digital balance will not be profitable. It is because digital balance measures the mass of apples. The mass of any substance is constant. So, a kilogram apple at the mountain will still be a one-kilogram apple in terai. 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? Solution: Let mass of the earth is = M Let 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’ = GM (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.

Oasis School Science and Technology - 10 195 Exercises 1. Choose the best answer from the given alternatives. a. On which factors does the mass of an object depend? i. gravity ii. number of molecules iii. weight iv. gravitation b. What is the value of acceleration due to gravity (g) at the centre of the earth? i. 9.8m/s2 ii. 9.83m/s2 iii. 9.78m/s2 iv. 0m/s2 c. How tall is the bridge if a stone dropped from it reaches the water after 3 seconds? i. 44.1m ii. 14.7m iii. 19.6 m iv. 176.4m d. If the gravitational force acting on a 75 kilogram object at 6400 kilometres away from the centre of the earth is 735 N, what would be the weight of an object? i. 9.8 m/s2 ii. 735 N iii. 75 N iv. 20 N e. If the weight of an object on earth is 100N, how much does it weigh on the moon? i. 100 N ii. 10.20 N iv. 17.04 N iv. 16.7 N f. What is the property of a freely falling object? i. velocity increases equally every second ii. acceleration increases equally every second iii. uniform velocity iv. zero acceleration 2. Define the following terms with required examples. a. Force b. Gravitation c. Newton’s law of gravitation d. Universal gravitational constant e. Gravity f. Gravitational field g. Acceleration due to gravity h. Mass i. Weight j. Freefall k. Weightlessness 3. Answer the following questions in very short. a. What are the factors affecting gravity? b. What is the relation between the gravitational force acting between any two objects with their masses and the distance between their centres? c. What is the average value of acceleration due to gravity on the surface of the earth?

196 Oasis School Science and Technology - 10 d. In which condition does an object fall freely? e. In which condition does a body of a certain mass become weightless? f. What happens to the acceleration due to gravity if an object moves away from the surface of the earth? g. What is the cause of the weight of an object? h. What happens to the gravitational force between two stones if they are taken to the moon, keeping the distance and mass constant? i. What will be the acceleration of a freely falling object on earth? j. Write the conclusion of the coin and feather experiment. k. What is the SI unit of gravitation? 4. Give reasons. a. Newton’s law of gravitation is called universal law. b. It is easier to lift a small stone but harder to lift a bigger one on the surface of the earth. c. The weight of a body is slightly more in the Terai and less in the Himalayan region. d. The weight of a body of a certain mass becomes zero in space. e. The probability of getting hurt is more when jumped from a taller place. f. Astronauts feel weightless inside spacecraft in outer space. g. Tides are taller in the ocean during the full moon. h. Jupiter is 317 times more massive than the earth but its acceleration due to gravity is 2.4 times greater than that of the earth only. i. Acceleration due to gravity is maximum at the surface of the earth. j. Objects fall faster at the poles than at the equator. k. Coin and feather fall together on the moon but not on the earth. l. Acceleration due to gravity varies from place to place on the earth. m. Acceleration due to gravity decreases in the coal mines. n. Weight of an object is more at the poles than at the equator. o. A person using a parachute can land safely. p. Mass of an object on earth is same even when it is measured on the moon. 5. Differentiate between the following. a. Free fall and weightlessness b. Gravity and acceleration due to gravity c. Gravitation and gravitational constant d. Mass and weight e. G and g 6. Answer the following questions in short. a. When a feather and a coin are dropped towards the surface of the earth, do they reach the ground together? b. Mention any three consequences of gravitational force. c. What are the applications of Newton’s law of gravitation?

Oasis School Science and Technology - 10 197 d. What happens to the gravitation between two objects if their mass is doubled keeping the distance between them constant? e. What happens to the gravitation between two objects if the distance between them is doubled, keeping the masses constant? f. Whenever a miner comes up through the mines, his load becomes heavier. How would you explain it? g. Why do the rivers flow? Does the gravity of the earth have any role in it? Discuss. h. Write the nature of Newton’s law of gravitation. i. What would be the gravitational force if the mass of one of the objects is doubled? j. What does it mean by the value of acceleration due to gravity at the surface of the earth is 9.8m/s2 ? k. What happens to the weight of a person if he travels from the Terai to the Himalayan region? Does it remain constant or change? Explain. l. What is the condition for weightlessness? m. Which part of the earth has the maximum weight of an object? 7. Answer the following questions on the basis of the given figure. Write any two effects of gravitational force. The earth’s orbit is oval. Explain how the magnitude of the gravitational force between the earth and the sun changes as the earth moves from position ‘A’ to ‘B’ as shown in the figure alongside. 8. Answer the following long questions. a. Write any two applications of gravity. A stone is dropped freely from 45 m height of the tower, it reaches the ground in 3 seconds. Calculate the acceleration due to the gravity of that stone. b. Derive the equation F = Gm1 m2 d2 , where letters have usual meanings. c. Prove the relation g ∝ 1 R2 , where letters have usual meanings. d. Write the effects of gravity. e. 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. 9. Numerical a. If a spring balance with the iron ball is released, what reading does the spring balance record and why? If the mass of the sun is 2×1030 kg, that of the earth is 6 × 1024 kg and the distance between them is 1.5 × 1011 m. What is the gravitational force produced between them? (G = 6.67 × 10-11 Nm2 /kg2 ). (Ans: 3.557×1022N) B A Sun Earth

198 Oasis School Science and Technology - 10 b. What do you understand by ‘weightlessness due to freefall'? The mass of the earth is 6 × 1024 kg and its radius is 6400 km, what will be the acceleration due to gravity at a distance of 3600 km far from the earth’s surface? (Ans: 4.002 m/s2 ) c. In which condition does the value of gravitation become equal to that of the gravitational constant? The radius of the earth is 6380 km and the height of Mt. Everest is 8848m. If the value of acceleration due to gravity on the top of Mt. Everest is 9.77 m/s2 , calculate the value of acceleration due to gravity on the surface of the earth. What is the weight of a body of mass 50 kg on the top of Mt. Everest? (Ans: 9.8 m/s2 , 488.5 N) d. Atmosphere is present around the surface of the earth but it is not present around the surface of the moon, why? The mass of Jupiter is 1.9 × 1027 kg and its radius is 7.1 × 104 km. Calculate the acceleration due to gravity on the surface of Jupiter. What will be the weight of a person of mass 85 kg on that planet? (Ans: 25.13 m/s2 , 2136 N) e. How would a parachute fall on the surface of the moon? Describe, the mass of Jupiter is 1.9 × 1027 kg and that of the sun is 2 × 1030 kg. If the gravitational force acting between them is 4.166 × 1023 N, calculate the distance between their centres. (Ans: 7.8 × 1011m) f. To estimate the height of a the building, a stone is dropped freely from the roof. The stone takes 1.5 seconds to reach the ground. Calculate the height of the building. Take g = 9.8m/s2 . (Ans: 11.025 m) g. If the mass of the earth is 5.97 × 1024 kg and its radius is 6371km meters. Calculate gravitational force between earth and a unit mass on its surface. h. Calculate the gravitational force between the earth and its satellite the moon, which is 3.84 × 105 km far, if their respective masses are 5.97 × 1024 kg and 7.34 × 1022 kg. i. 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. j. If Nancy can lift 50 kg in earth, how much can she lift on Jupiter? If acceleration due to gravity of the earth and Jupiter is 9.8m/s2 and 25.1m/s2 respectively. k. Radha shot a paper rocket upward, it gained maximum height of 35 meters. Calculate the time required to reach that height and also find the initial velocity of the paper rocket.

Oasis School Science and Technology - 10 199 Key terms and terminologies 1. Pressure : The thrust per unit area of a surface is called pressure. 2. Thrust : The total perpendicular force exerted by a body on the surface is called thrust. 3. 1 Pascal pressure : The pressure exerted by 1N force acting normally upon the area of 1m2 is called 1 pascal pressure. 4. Liquid pressure : The thrust exerted by a liquid per unit area of the base and wall of the container is called liquid pressure. 5. Pascal’s law : Pressure is transmitted equally in all directions when pressure is applied at a place on a liquid kept in a closed container.” 6. Principle of 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." 7. Upthrust : The resultant upward thrust exerted by a fluid is called upthrust. 8. Archimedes' principle : Archimedes' principle states, "When a body is partially or wholly immersed in a fluid, it experiences an upthrust which is equal to the weight of the fluid displaced by it.” 9. Law of flotation : The law of flotation states, “A body floats on a liquid if it can displace the liquid equal to its own weight.” 10. Hydrometer : A hydrometer is a device used to measure the density of a liquid or relative density of a liquid. UNIT 8 PRESSURE Estimated teaching periods Theory 4 Practical 1 • Introduction to pascals law and its application in daily life activities • Introduction toupthrust • Introduction and application of Archimedes' principle The Sequence of Curriculum Issued by CDC 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. About the Scientist Archimedes of Syracuse

200 Oasis School Science and Technology - 10 Introduction The school bags have wide straps so that less pressure is put on the hand while carrying them. The weight of the train is spread out over a large area by putting the tracks on large sleepers. It puts less pressure on the ground. It is painful to walk with bare feet on gravelled road. It is due to the fact that our body is based on a small area on the ground and there is large pressure on our feet. a. b. c. Fig. We find it easy to chop vegetables with a sharp knife as it exerts more pressure on the vegetables. Food is cooked faster in a pressure cooker than in an open pot due to higher pressure inside the pressure cooker. Similarly, a helicopter can fly in air because the fans of the helicopter keep the air pressure below them higher than above during the flight. Water flows at high speed in the tap downstairs than in upstairs. These examples justify the existence and utility of pressure in our daily life. The thrust per unit area of a surface is called pressure. The pressure exerted by air is called atmospheric pressure. It is very useful for us as it helps to fill ink in pen, to fill medication in a syringe, to lift underground water, to inflate the tyres of vehicles and so on. In this unit, we will study liquid pressure, various laws related to pressure (Pascal's law, Archimedes' principle, law of flotation) and atmospheric pressure. Thrust When a body is placed on a surface, it exerts a force on that surface. The total perpendicular force exerted by a body on the surface is called thrust. The effect of thrust depends on the area of the surface on which the thrust is applied. Since thrust is a force (F), it is measured in newton (N), dyne, etc. It is a vector quantity. Fact File Studs are made on the sole of a football player's boot. Studs are made on the sole of a football player's boot to increase the pressure on the ground which prevents the player from falling or sliding. Fact File The rear wheels of a tractor are made large and flat. The rear wheels are made larger and flat to reduce the pressure. It prevents the tyres from sinking into the muddy land. Units of thrust SI unit CGS unit newton (N) dyne