SPECIAL FEATURES OF GRAVITATIONAL FORCE

     The gravitational force between two bodies constitute on action and reaction pair. If the force exerted by the mass m1 and mass m2 is called action. Then the force exerted by the mass m2 on the mass m1 is to be called reaction. Clearly, these forces are equal in magnitude but oppositely directed.                                                                      

 

1) The gravitational force between two bodies does not depend upon the nature of the intervening medium. This rule out the possibilities of making gravity screens. The gravitational force between two bodies of masses m1 and mass m2 are same whatever be the medium like air, water, glass etc. between them. That is, we cannot alert the value of gravitational force between two bodies without varying their mass and distance between their centers. Thus, gravitational force between two bodies does not depend upon the or absence of others bodies in between other nearby these bodies

 The gravitational force between light bodies is extremely small and hence such smaller force is not felt in practice. However, it becomes appreciable in the case of massive bodies. This is clear from the following example:

Suppose your friend have the same mass of 40 kg and are standing at the separation of 1 m. The mutual force of attraction between you is given by,

                 =6.67×10ˉˡˡ×40×40/ (1)²

                 = 1.067×10-7N

This is a force of negligible magnitude in our daily life. Thus, the gravitational force between you and you friend does not stick you and your friend standing nearby.

The distance between the sun and the earth is about 1.5×10-7 km. The gravitational force between then is of the order of 10-7 km. The gravitational force between then is of the order of 1027 N, which cannot be ignored. Thus, the earth revolves around the sun due to the gravitational force of such large magnitude.

 

EF       EFFECTS OF GRAVITY

Gravity plays a vital role in our everyday life as well. Some of the effects are as follows:

1)   We are able to stand up, run and perform other activities freely due to gravity of the earth. On the surface of the moon, we cannot push a body as done on the surface of the earth; otherwise the body gets thrown away in space and never returns again to the surface of the moon. This is because of small gravity of moon.

2)   Construction of building and bridges is possible due to the gravity of the earth.

3)   There will be no atmosphere around the earth in the absence of gravity of the earth. Thus, it makes life possible on the earth. There will be no season change without atmosphere .as the gravity of the moon is very small, it does not have atmosphere.

4)   If a body is thrown upwards, its motion is opposed by gravity of the earth. So, it falls back to the earth.

5)   Tides occur by the gravity of the moon on ocean water. As mass of ocean water is grater, there is more force of gravity in between the water and the moon. It results the pull of water due to which ocean level increases and tide occurs. The flowing property of liquid also supports the process.