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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

**Davide ** Asks:

**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)

**Answer**:

I must congratulate you first for thinking deep and differently.

The relativistic increase in mass is given by the equation

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.)*