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## Gravity on moon

We know that the first man to walk on moon was Neil Armstrong. it is said that there is  no force of gravity on moon. then how did Neil Armstrong moved a few steps on moon?

Who says there is no gravity in moon?

The acceleration due to gravity on moon is 1/6 that on earth.

I feel that you are confused by the concept of weightlessness in satellites.

On moon, it has its own gravity which is one sixth that on earth.

## Is linear momentum conserved when a ball is thrown vertically up in the sky?

ROUNAK BHATTACHARJEE asked the above question.

The fact is that linear momentum is conserved in all interactions. If you concentrate on the motion of a single body alone, that will not account for an interaction. When thrown above, according to the principle of conservation of momentum, what we can say is that “The total momentum of the ball plus the thrower just before throwing is equal to the total momentum just after throwing”

After that what happens is controlled by the force of gravity acting on it. The force acting on it can change the momentum. Here the interaction is between the ball and the earth. On account of the huge mass of earth, the motion of earth to compensate the motion of ball and to conserve the momentum cannot be detected.

However, the linear momentum is conserved in all events and interactions so far!

## 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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