# The Naked Scientists Forum

### Author Topic: What stops the Moon falling to Earth?  (Read 1556 times)

#### thedoc

• Sr. Member
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##### What stops the Moon falling to Earth?
« on: 14/11/2013 12:30:02 »
Scott Borthwick  asked the Naked Scientists:
Why doesn't Earth and Moon gravitate towards each other like two magnets? Is it centrifugal force keeping these two bodies apart?

Greetings from Cape Town. Awesome show with Redi every Friday.

Cheers,
Scott

What do you think?
« Last Edit: 14/11/2013 12:30:02 by _system »

#### Pmb

• Neilep Level Member
• Posts: 1838
• Physicist
##### Re: What stops the Moon falling to Earth?
« Reply #1 on: 14/11/2013 12:38:50 »
Quote from: thedoc
Why doesn't Earth and Moon gravitate towards each other like two magnets? Is it centrifugal force keeping these two bodies apart?
Yes, it's the centrifugal force just with anything in orbit around the earth.

#### spartaman64

• First timers
• Posts: 9
##### Re: What stops the Moon falling to Earth?
« Reply #2 on: 15/11/2013 02:57:17 »
The moon is moving fast so the edge of the earth is falling away faster than the moon can fall. If you throw a baseball really hard and it moves really fast it will go over the curve of the earth before it hits the earth and it will keep on going in orbit.

#### David Cooper

• Neilep Level Member
• Posts: 1505
##### Re: What stops the Moon falling to Earth?
« Reply #3 on: 15/11/2013 18:30:39 »
The moon's doing it's best to hit us, but it just keeps missing. In a system of two objects, it turns out that if they don't collide the first time they approach each other, they will either separate and never come back together or else they end up in a stable orbit. [There are a few qualification to that: orbits gradually decay due to the curvature of space around massive objects (if General Relativity is correct, but the decay will still happen even if some other theory replaces it); tidal effects are driving the moon further away from the Earth, to the point that its orbit will become elongated and eventually it will collide with the Earth (though I think that depends on interaction with the Sun as well) though this collision will be prevented if the Sun expands enough to destroy them both first; and a planet going round a star can orbit further out over time as the star loses mass. Other things can affect orbits if there are more than two objects involved, such as the pull of other planets and drag from gas.]
« Last Edit: 15/11/2013 18:32:40 by David Cooper »

#### The Naked Scientists Forum

##### Re: What stops the Moon falling to Earth?
« Reply #3 on: 15/11/2013 18:30:39 »