•Gravitation -
The force exerted by the object and the earth on each other is called as gravitation. This attractive force is directed towards the centre of earth.
• Circular motion and centripetal force-
The rotation of object along a circular path is called as circular motion. The force acting on any object in a circular motion which is directed towards the centre of the circle is called centripetal force.
• Kepler's laws of planetary motion-
1) The orbit of a planet is an ellipse with the sun at one of the foci.
2) The line joining the planet and the sun sweeps equal areas in equal intervals of time.
3) The squre of its period of revolution around the sun is directly proportional to the cube of the mean distance of planet from the sun.
• Newton's universal law of gravitation -
According to theory of universal gravity, every other object with a definite force. This force is directly proportional to product of masses of two objects and inversely proportional to squre of distance between them.
• Magnitude of centripetal force -
When an object is constantly acted by force directed towards the centre of circle, this force is called centripetal force.
The acceleration caused by the gravitational force due to earth on the body is called earth's gravitational acceleration denoted by 'g'. h = 9.77 m/s*2 and it depends only on mass 'm' and radius 'r' of earth.
• Variation in value of 'g' -
1) Change along surface of earth - Value of 'g' highest at poles (9.832) , decreases with decreasing latitude and lowest at equator (9.78).
2) Change with height - Value of 'g' decreases with increases in hight from surface of earth.
3) Change with depth - Value of 'g' decreases as we go deep inside the earth.
• Mass and Weight -
1) Mass - mass is the amount of matter present in object. It is also the measure of inertia of object. SI unit is Kg, It's scalar quantity.
2) Weight - weight of object is defend as the force with which the earth attracts the object.
• Free fall -
When an object moves under influence of force of gravity along, it is said to be falling freely. For free fall, u = 0 and a = g
• Gravitational potential energy -
Gravitational potential energy is the energy stored in an object because of its position in a gravitational field .
• Escape velocity -
Escape velocity is the minimum speed needed by an object to escape from the gravitational force of earth for an object of mass m.
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