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Q & A: Earth's spin and gravity

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Most recent answer: 07/29/2012
Q:
A friend of mine told me once that the spinning of the earth is the thing keeping the sea from flowing out into space. When I ask him to give me a proof he swings a bucket of water around his head to show me that the water doesn't flow out, I keep explaining him that the spinning pushes things away from earth and the gravity is the thing keeping everything together but he is opinionated ,he tells me that if the earth wasn't spinning the sea water would flow out ! and he mix things up when he asks me why the moon effect on the sea beats the effect of the earth on it. So I ask you to provide me with a clear EXPLANATION for this issue,is there any relation between gravity and spinning and is the bucket of water a proper example. my friend's name is mesut, and another one named sherif stand with him along with a physic teacher called Abd El-haq, I mentioned the names only to show them this later so forgive me. and thanks !
- benbraika (age 18)
Algeria
A:
We've gotten a very similar question to this before:
 

It's quite puzzling that people keep thinking the spin somehow causes the gravity. We really have no idea why anyone thinks that.

I'm not sure I would say exactly that the spinning "pushed things away from the Earth", but since things do tend to keep moving in straight lines, stuff does tend to fly off of spinning objects. Your friends could put some water on a bicycle wheel and spin it to see that effect.

It is interesting that the Gravity Probe B experiment finally succeeded in measuring the tiny effects of the Earth's spin on gravity. Essentially all the gravity, however, comes from the Earth's mass itself.

Mike W.

(published on 07/29/2012)

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