Science Questions

Is gravity around the planet constant?

Sun, 5th Nov 2006

Part of the show Naked Science Q&A and Record Breaking Fireworks

Question

Andy on the A120 asked:

Is gravity around the planet constant? If you have a spinning ball and put a penny on it, it will be thrown off at the equator but not at the pole.

Answer

Gravity is nothing to do with rotation. If the earth were a perfect sphere, gravity would be the same in all directions. As the earth is actually slightly flattened, gravity will be slightly larger at the poles. What the rocks are below you also makes a difference. If you are on a very dense piece of rock, gravity will be slightly higher. Of course, if you are interested in how much you will appear to weigh, centrifugal force will also have an effect so you will appear to weigh less than you would do if the earth wasn't spinning.

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