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1. GRAVITATION

   10th Grade – Physics 10th - Physics
2. INTRODUCTION Whyis Moon goingaround the earth in a circularorbit? Whydoesntitfall down to the earth? Whydoesntit go awayfromearth? 10th - Physics
3. Newton and the Apple Sir Isaac Newton gotanswers for all these questions, whenhewassittingunder an appletree. He explained the answers for these questions as Universallaw of gravitation 10th - Physics
4. Thelaw ofGravitation WhatmadethatApplefallto theground? Everyobject onthesurface oftheEarth isattractedtowardsthecenter oftheEarth. Thisforce iscalled asGravitationalforce. The gravitational force is directly proportional to the mass of the object. The gravitational force is inversely proportional to the square of the distance between the objects. This helps us arrive at the formula 2 Where- massof theobject d - distancefromthecentre oftheEarth 10th - Physics
5. Thelaw ofGravitation The object exerts an equal and opposite force on the Earth 2 Where is the mass of the Earth Combining the two equations, we get 2 Newton Generalized that there is a force between any two objects and proposed his universal law of Gravitation , Every particle in the universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them. This force acts along the line joining the two particles. 10th - Physics
6. The law of Gravitation where: F1,F2are the force between the masses, G is the constant of proportionality m1 is the first mass, m2 is the second mass, and r is the distance between the centers of the masses. G is called as the universal Gravitational constant. It has the same value for all the objects. Its accepted value is 6.67 x 10-11Nm2kg-2 10th - Physics
7. Thelaw of Gravitation The centripetal force provided to the Moon is the gravitational force given by the formula 2 Gravitational force is independent of: Intervening Medium and their masses Change in temperature, Pressure or any other physical condition The law is valid for small and large masses and distances Holds good for celestial bodies also Hence the law of gravitation is an universal law , Here - mass of the object - mass of the Earth d - distance from the centre of the Earth 10th - Physics
8. Weight and Weightlessness Weight(W) of an object with mass m is given by the formula wheregis the acceleration due to gravity at the Earth’s surface We exert a Gravitational force on the Earth. The ground in turn provides an equal and opposite reaction. This reaction is weight. This force called weight is defined by the universal law of gravitation as: where is the Mass of the Earth Hence, mg g = , 10th - Physics
9. Weight and Weightlessness Astronauts experience Weightlessness when their space craft orbits around the Earth. The gravitational pull is used in providing the necessary centripetal force to the space craft. Due to the centripetal force, there is no reaction on the occupant in a space craft. This condition of zero reaction is called Weightlessness. , The value of g at a distance of 3.84 x 105 km (distance of the moon), the value is found to be nearly 2.7 x 10-3 ms-2 10th - Physics
10. Variation of ‘g’ If a body is at a height h above the ground, then the value of gravity , the acceleration due to gravity is given by: Value of g is independent of mass of the object, but depends on the mass of the Earth and the distance of the object from the Earth Value of g is slightly higher at the poles and than that at the equator, because of the geoid shape of the Earth 10th - Physics
11. Motion of planets around the Sun Johannes Kepler is best known for his discovery of the three laws of planetary motion. These laws are based on his observations and the data collected by Tyco Brahe. Kepler’s First Law: 10th - Physics
12. Motion of planets around the Sun Kepler’s Second Law: 10th - Physics
13. Planets around the Sun Kepler’s Third Law: 10th - Physics
14. Planets around the Sun Kepler’s third law can be used to find Mass of the sun Distance of a planet Period of revolution of a planet Newton showed that Kepler’s laws can be derived from the universal law of gravitation. , Centripetal force = gravitational force mv2/r = v2 = But v = 2 2 = GM/r 10th - Physics
15. Importance of the law of Gravitation The law of gravitation successfully explained several phenomena: The force that binds us to the Earth The motion of moon around the Earth The motion of planets around the sun The tides due to the Moon and the Sun The law of gravitation successfully predicted The existence of planets beyond the Uranus Observations in the deviations in the orbit of Uranus led to the discovery of Neptune in the nineteenth century Smaller deviations in the orbit of Neptune led to the discovery of Pluto in 1930 Pluto though was initially considered as planet, now has been given the status of a dwarf planet, because of its size which is only twice of its Moon. , 10th - Physics
16. Exercise State the universal law of Gravitation What led Newton to develop the law of Gravitation? Why is the law of gravitation called a universal law? What is weight? How does the acceleration due to gravity vary with height? Explain Mention three points successfully explained by the law of Gravitation What led to the discovery of the planet Neptune? What led to the discovery of planet Pluto? What is meant by Weightlessness? Explain with an example. , 10th - Physics