Page 1 : 1) Gravitation :, Gravitation is the force of attraction between two objects in the, universe., , i) Gravitation may be the attraction of objects by the earth., , Eg :- If a body is dropped from a certain height, it falls downwards, due to earth’s gravity., , If a body is thrown upwards, it reaches a certain height and then, falls downwards due to the earth’s gravity., , ii) Gravitation may be the attraction between objects in outer space., Eg :- Attraction between the earth and moon., Attraction between the sun and planets., , Centripetal force :, When a body moves in a circular path, it changes its direction at, every point. The force which keeps the body in the circular path acts, towards the centre of the circle. This force is called centripetal force., , If there is no centripetal force, the body will move in a straight line, tangent to the circular path.

Page 2 : 2) Universal law of gravitation :, The universal law of gravitation states that, ‘Every object in the universe, attracts every other object with a force which is directly proportional to product, of the masses and inversely proportional to the square of the distance between, them.’, , F, M m, d, , Let two objects A and B of masses M and m lie at a distance d from each other., Let F be the force of attraction between them., According to the universal law of gravitation the force between the objects is, , directly proportional to the product of their masses and inversely proportional, to the square of the distance between them., , 1 Mxm, FaMxm and Fa --- Combining the two equations Fa ---------& d?, Mxm, Or F=G --------- where G is a constant of proportionality called, d? universal gravitation constant, rie, , Cross multiplying we get Fxd?=GMxm or G& -------Mxm, , The SI unit of Gis N m* kg * andits value is 6.673 x 107'N m? kg 7

Page 3 : 3) Free fall :, The earth attracts objects towards it due to gravitational force. When an, object falls towards the earth due to the earth’s gravitational force it is called, free fall., , When an object falls towards the earth there is a change in its acceleration, due to the gravitational force of the earth. So this acceleration is called, acceleration due to gravity., , The acceleration due to gravity is denoted by g., The unit of g is same as the unit of acceleration ms ?, From the second law of motion, force is the product of mass and acceleration., , F=ma, For free fall, force is the product of mass and acceleration due to gravity., , M, F=mg or mg=G or g=G---- where M is the mass of the, d?2, where M is the mass of the earth and d is the distance between the object and, the earth., , For objects near or on the surface of the earth d is equal to the radius of the

Page 4 : 4a) Mass :The mass of a body is the measure of its inertia. If the mass of a, , body is more its inertia is more., , The mass of a body is constant and does not change from place to, place., , The SI unit of mass is kg., , b) Weight :The weight of a body is the force with which the earth attracts the, body., , The force with which a body is attracted by the earth depends on its, mass m and acceleration due to gravity g., , F=mxg, Since weight of a body is the force with which the earth attracts the, body, W=mxg, , Since g at a place is constant, Wa m, The weight of a body changes from place to place., The SI unit of weight is the same as force — Newton (N).

Page 5 : c) Weight of an object on the moon :, Celestial Mass (kg) Radius (m), body, , Earth 5.98x 10% 6.37 x 10°, , Moon 7.36 x 107 1.74 x 10®