# Gravity relies on rotation

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1. Jan 24, 2017

### Clubbes

1. The problem statement, all variables and given/known data
I do not know if this is the right forum to be asking this, but it is the best i have found.

A classmate of mine came with the statement that if the earth stopped spinning we would all float off to space because the earths mass is to small to able to hold everyone down.
I am reluctant to believe this as my limited understanding of physics says that mass is the decider of the strength of gravity, not that it need to rotate aswell.

The question is, if the earth and everyone on it lost its momentum. would we still be on earth? or would we float out to space.
This question is not taking into consideration that we would either freeze or burn since the sun would cook one side and the other side would freeze. (please correct me on this if i am wrong.)

2. Relevant equations

3. The attempt at a solution

2. Jan 24, 2017

### haruspex

I suspect someone has misunderstood a claim and constructed their own spurious explanation.
The original may have been "if the Earth suddenly stopped spinning then we would all fly off nto space because of our own momentum".
Even then, it is wrong. It would certainly be unpleasant, but Earth's gravity is much stronger (about 30 times as strong) as the centripetal force required to keep us on terra firma.

3. Jan 24, 2017

### CWatters

+1

They are very confused. Spinning doesn't produce a force that "holds people down". If it did then mud wouldn't fly off a car/bike wheel. On the contrary.. spinning requires a force (centripetal force) to make things move in a circle and stop mud or people flying off. So someone on a spinning planet appears to weigh slightly less than someone on a non spinning planet.

If your friend was correct, what would happen to someone when they reach the north pole?