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# Tag Archives: gravitational force

## Why gravitational force of attraction is necessary for a satellite to revolve around earth?

The question was posted by Raj Kumar.

The satellite has a velocity. To revolve around, the direction of velocity must change. In the absence of a force it can move only in a straight line. It is the gravitational force which helps the satellite top change direction and revolve around the earth.

In other words, for a satellite to revolve in a circular path, a centripetal force is required. This centripetal force is provided by the force of gravitation only.

## Weight of a freely falling body

What is the weight of a body having a mass of 10 kg if it is falling freely?

Answer: The apparent weight of a freely falling body is zero.

When a body falls freely, it is falling with an acceleration =g. Thus the entire gravitational force acting on it is utilized in accelerating it and hence its weight is not felt.

## Effect of Relativity on Gravitation

I wonder, If we take atoms travelling with speeds close to that of light, there will be an increase in mass (according to the theory of [wiki]relativity[/wiki]).  As the mass increases, the gravitational force should also increase.  Will this increase in [wiki]gravity [/wiki]affect the surrounding space?

If an atoms travels with 99% the speed of light, what will be its increase in mass?

(The question was reformatted to suit the language)

I must congratulate you first for thinking deep and differently.

The relativistic increase in mass is given by the equation $m=\frac{m_{0}}{\sqrt{1-\frac{v^{2}}{c^{2}}}}$

The increase in mass increases the gravity, but the force of gravity is governed by the value of the universal constant of gravitaton, which is very low (6.67 x 10-11).

For the second part of your question, the increase in mass can be calculated to be about 7 times from the equation mentioned above.

(Please post your further doubts on this topic as comment to this post so that all related ideas come together.)

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