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Chapter 1 force
- 1. Grade 10 Force Preparedby Bhuvan Acharya Push or pull of an object is considered a force. Push and pull come from the objects interacting with one another. Terms like stretch and squeeze can also be used to denote force. In Physics, force is defined as: The push or pull on an object with mass that causes it to change its velocity.
- 2. Common symbols: F→,F SI unit: Newton In SI base units: kg·m/s2 Other units: dyne, poundal, pound- force, kip, kilo pond Derivations from other quantities: F = m a Dimension: LMT-2 Common symbols: F→, F SI unit: Newton In SI base units: kg·m/s2 Other units: dyne, poundal, pound- force, kip, kilo pond Derivations from other quantities: F = m a Dimension: LMT-2 The Force can be measured using a spring balance. The SI unit of force is Newton(N). Test your Knowledge o
- 3. Test your Knowledgeon Force Which of the following forces is responsible for making the moon revolve around the Earth? • A)Magnetic Force • B)Electric force • C)Frictional Force • D)Gravitational Force
- 4. Which of thefollowing statements is true about force? • A)Force is the push or pull on an object resulting from the object's interaction with another object. • B)Force is defined as mass per unit volume. • C)Force is the ability to do work. • D)The movement of charged particles is known as force
- 5. Gravitation • The forcebetween any two bodies is called gravitation. • Before 1542AD, The earth is considered to be the centre of solar system.This earth centered model of the solar system is called geoentric or ptolemaic model. • In 16th century Nicholas Copernicus , put forward heliocentric model in which The Sun was the head of solar system.
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- 8. Newtons law ofGravitation Newton’s Law of Gravitation states that “The force of attraction between the two bodies is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.”This law was formulated in 1687 AD.
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- 10. Verification of Newton’slaw: Consider the two bodies of the mass M1 and M2with force F acting between them towards their centre. If the distance between their centers is d then, • According to Newton’s universal law of gravitation, We have F ∝ m1m2……1) and F ∝ 1/d2……… 2) Combining 1 and 2 we get 𝑜𝑟, 𝐹 ∝ 𝑚1𝑚2 𝑑2 Or,𝐹 = 𝐺 𝑚1𝑚2 𝑑2 • Where G is proportionality constant which is known as universal gravitational constant.
- 11. Definition of G •We have , • 𝐹 = 𝐺𝑚1𝑚2 𝑑2 • If m1=m2 =1kg and d= 1m.Then • 𝐹 = 𝐺1𝑋1 12 • 𝐹 =G • The universal gravitational constant can be defined as the force of gravitation produced between two bodies of unit mass each which are separated unit distance apart.
- 12. Properties of G: •Value of G is independent of the temperature, pressure, nature of the intervening medium and chemical composition of the masses of the bodies. • The numerical value of gravitational constant (G) is 6.67x10-11 and • Its unit is Nm2/Kg2
- 13. Newton’s law ofgravitation is called universe law ,why? Newton’s law of the gravitation holds true or applicable for all the objects present in this universe whether the objects be terrestrial or celestial. The gravitational force exists everywhere in this universe. Therefore Newton’s law of gravitation is called universe law.
- 14. To Know therelation between gravitational force , mass and distance. Sol. Let us consider two bodies of masses m1 and m2 which are kept d distance apart. Then the gravitational force between them is given by F= 𝐺𝑚1𝑚2 𝑑2 If masses of each are doubled then Fnew= 𝐺2𝑚1𝑥2𝑚2 𝑑2 = 4𝐺𝑚1𝑚2 𝑑2 =4F Therefore the new gravitational force increases by 4 times when mass of one body is doubled.
- 15. Q.N 2. WhatChange occurs to the gravitational force between two body when masses of each body doubled keeping distance constant? Sol. Let us consider two bodies of masses m1 and m2 which are kept d distance apart. Then the gravitational force between them is given by F= 𝐺𝑚1𝑚2 𝑑2 If masses of each are doubled and distance is kept constant. Fnew= 𝐺2𝑚1𝑥2𝑚2 𝑑2 = 4𝐺𝑚1𝑚2 𝑑2 =4F Therefore the new gravitational force increases by 4 times when mass of one body is doubled.
- 16. Q.N 2. WhatChange occurs to the gravitational force between two body when masses of each doubled and distance tripled? Sol. Let us consider two bodies of masses m1 and m2 which are kept d distance apart. Then the gravitational force between them is given by F= 𝐺𝑚1𝑚2 𝑑2 If masses of each are doubled and distance is tripled. Fnew= 𝐺2𝑚1𝑥2𝑚2 (3𝑑)2 = 4𝐺𝑚1𝑚2 9𝑑2 = 4 9 F Therefore the new gravitational force decreases by 4 times when mass of one body is doubled and distance is tripled.
- 17. Importance of gravitationalForce • Binding all terrestrial objects. • Holding the atmosphere on the planets. • Rainfall and snowfall . • Flow of water in river • Motion of the planets in their respective orbits.
- 18. Characteristics of gravitationalforce • It is independent of the nature of intervening medium. • It is independent of presence or absence of other bodies. • It is independent of the nature and size of the bodies. • It is central force and acts along the line joining the centres of two bodies.
- 19. Numericals • .Mass ofEarth is 6x1024 kg and mass of the Sun is 2x1030 kg and the distance between them is 1.5x1011 m. Calculate the gravitational force between them. • .Mass of Earth is 6x1024 kg and mass of the moon 7.1x1022 kg and gravitational force between them is 1.682x1020 N ,find the distance between them.
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- 21. Gravity • Gravity isa special case of gravitation. • The force with which the earth pulls a body towards its centre is called Gravity. • F= 𝐺𝑀𝑚 𝑅2 • Its SI unit is Newton.
- 22. Comparison of gravityof different planets • The gravity of the moon is 1/6th of the earth. • The Jupiter is the largest planet of the solar system.The mass of the Jupiter is about 319 times greater than the earth and radius is 11 times more than the earth.The gravity of the Jupiter is 2.5 times more than the earth.
- 23. Acceleration due togravity • The acceleration produced on a body due to gravity is called acceleration due to gravity. • Its SI unit is 𝑚 𝑠2. • The acceleration due to gravity on the moon is 1.66m/s2. What does it mean?
- 24. Coin and Featherexperiment • Galileos arguments were experimentally tested by the British Scientist Robert Boyle. Boyle performed an experiment to verify Galileos idea that a light object and heavy object fall together in vacuum. • Conclusion of the coin and feather is that the acceleration produced in the freely falling objects is same and does not depend on the masses of the falling objects.
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- 29. Home assignment 1)The radiusof the moon is 1.17𝑥106 m and its mass is 7.2𝑥1022 kg. What is the gravity of the moon on the body with mass 1kg? 2) The radius of the Earth is 6.4𝑥106 m and its mass is 6𝑥1024 kg. What is the acceleration due to gravity of the earth. 3)What is the relationship between acceleration due to gravity of any planet with their radius? 4)Write the average value of acceleration due to gravity on the earth, moon and Jupiter. 5) The acceleration due to gravity on the earth is 9.8m/s2. What does it mean? 6)If your weight is 600N on earth, how far should you go from the centre of the earth so that your weight will be 300N.(radius of the earth is 6.4x106m) 7)The mass of earth is 6x1024 kg and radius is 6.4x106m.Calculate the value of acceleration due to gravity of the earth. 8)The mass of eath is 6x1024 kg and radius is 6.4x103km.Calculate the value of acceleration due to gravity at the top of Mt Everest .Also calculate weight of a body having 80 kg. 9)The value of acceleration due to gravity on the surface of the earth is 9.8m/s2.Calculate the value of acceleration due to gravity at the top of 1000Km from the earth surface. 10)A stone dropped freely from 72m height of the tower and reaches the ground in 6 seconds . Calculate acceleration due to gravity of that stone.
- 30. Comparison of massand weight Mass • The quantity of matter contained in a body. • It is scalar. • Its SI unit is kg. • It is constant everywhere. • It can not be zero. • it depends on no. of molecules and their mass. • It is measured with the help of beam balance. Weight • The force with which the body is attracted towards the center of the earth. • It is vector. • Its SI unit is Newton. • Its value changes with the change of value of g. • It may be zero. • It depends on value of g and mass. • It is measured with the help of spring balance.
- 31. Freefall • The motionof a body under the influence of gravity alone is called freefall • Freefall occurs only in vacuum. • Fall with Parachute • Air exerts resistance on a parachute as a result it falls slowely and a person with parachute can jump safely from a greater height on the earth.But this is not possible on the moon because there is no air and air resistance.
- 32. Weightlessness • The stateof a body in which the weight of a body becomes zero is called weightlessness. • The state of weightlessness can be observed in the following cases. 1.Body in a freely falling lift. Because the lift moves down with acceleration equal to acceleration due to gravity i.e.,a=g W=m(g-a) =m(g-g) =0
- 33. 2.Body in asatellite orbiting earth • When a satellite is revolving around the earth, every object inside the satellite has acceleration equal to the acceleration due to gravity.
- 34. 3.Body at nullpoint • At the null point force of moon and earth are equal and opposite. And value of acceleration due to gravity is also zero so weight is zero at null point.
- 35. 4.Body at thecenter of the earth. • At the center of the earth value of acceleration due to gravity is zero so weight becomes zero.
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- 38. Verification of Newtonslaw of gravitation
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