How do planets spin and move simultaneously?

15 November 2009



What is it that keeps planets spinning, as well as keeping them moving in their orbits?”


We posed this question to Dr Matt Balme...

Well, it's a fairly simple piece of physics. One of the things that keep on moving their orbit, there's nothing to stop them! 

I mean, they're not hitting anything, so to speak. So they're not losing any energy, and they're not losing, more importantly, angular momentum.

So angular momentum is a conserved thing. It can't just be taken away by, just by wishing it away. It has to be taken away by things, and the Earth is just sitting there, rotating. Nothing's taking its angular momentum away except the Moon.

The Moon is actually going to steal some of the Earth's angular momentum, slow it down, and at some point in the future, the Earth and the Moon will be locked together they would both have lost angular momentum. At the moment, we only see one face of the Moon.

In the future, only one face of the Earth will be facing the Moon. So we'll only be able to see the Moon from one side of the Earth, and vice versa.


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