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TwoUglyFeet t1_iy7lii5 wrote

Reply to comment by Ripper209 in what would be different if we had two moons by Any_Palpitation_3110

Gravity. The moon pulls on the earth like two people holding a rope. This force is called tidal force and causes to water (and the earth) to move to side closest to the moon. These are what tides are.

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Ripper209 t1_iy7m41w wrote

In terms of general relativity, is this "rope" nonexistent? Are they just moving along curved paths caused by the mass of the moon and earth?

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TwoUglyFeet t1_iy7nlu4 wrote

The moon is in earth's gravity well. This bending is the reason we see the forces of the Earth and moon acting on each other.

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Ripper209 t1_iy7srji wrote

Thank you very much this was really helpful

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strange--alien t1_iy88lp4 wrote

If you imagine this scenario, having a tennis ball on a string and holding it above your head spinning it like a helicopter rotor. Generally speaking, the tennis hall represents a moon, rope is the gravitational tether between the two, and (with a bit of imagination) your hand are represents the earth. So, when spinning the tennis ball around, the mass of the tennis ball sets a limit on the speed of spinning. One rotation is an earth day. If you had a heavier ball like a basket ball (larger moon) the speed of rotation would be slower because the earth has to sling a heavier moon. Spinning a lighter ball like a ping pong ball (tiny moon) would be so easy that the tiny moon wouldn't have any affect on spinning speed basically. Smaller you get and the moon wouldn't be able to hold itself in the earth's gravity and would fling off in to space. To summarise, larger moon puts a brake on our earth's rotation, Smaller moon would ease pull back on our earth. Two moon's would be wack! Double the werewolves, double the astrology readings. Spooky

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Ripper209 t1_iy9mz4n wrote

This is exactly what I'm looking for thanks!

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strange--alien t1_iya1txe wrote

I could hear your unspoken question very clearly. Btw I messed up one piece. One tennis ball rotation is one moon orbit (27 days), not one day. Still same physical concept though.

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