everybody in the universe attracts every other body with a force which id directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres. this note provides us with an information about newton's law of gravitation .

Mass of a body is the quantity of matter contained in it. The effect of a force applied on a body depends on its mass. It has appeared in two entirely different contexts: Newton’s second law of motion and Newton’s law of gravitation. So meaning of mass is clear if we define mass as (i) inertial mass and (ii) gravitational mass

According to Newton’s law of gravitational, the force of attraction varies inversely as the square of the distance of the body from the centre of the earth. This shows that in the space all around the earth, its gravitational pull can be experienced by other material bodies. The same is true for other material body. The space around a material body in which its gravitational pull can be experienced is called gravitational field.

When an object is thrown upward, it reaches a certain height and comes back to the earth. If the body is given certain minimum initial velocity y from the earth’s surface, so that it goes beyond the gravitational field of the earth, than the velocity is said to be escape velocity. So the escape velocity is defined as the velocity which will take a body to go the infinite distance away above the surface of the earth when projected upwards. Weightlessness is a situation in which the effective weight of the body becomes zero. If a body mass m is lying at a location where the effective acceleration due to gravity is g’, then the effective weight of the body = mg’. The effective weight of the body will be zero is g’ = 0.

A satellite is a body which revolves continuously around a bigger body. The gravitational force between them provides the required centripetal force. There are two types of satellite and artificial satellite. Moon is the natural satellite of the earth. Artificial satellites are put into their respective orbits with the help of rockets.