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level 1
Numerical Simulations | Galaxies | ISM9 points · 1 month ago

The Moon is likely to have been from the Earth - Earth got hit by some large object early on, and the resulting mess consolidated into two bodies. So the original Earth would have been more massive, and had stronger gravity.

If you're asking about whether the gravity of the Moon pulls us "up" away from the Earth, making Earth's gravity comparatively weaker, then that's a bit more complex. The Moon is pulling us on the surface and the Earth at the same time. So the only effect is the difference between how much the Moon is pulling us on the surface versus how much its pulling the Earth as a whole on average.

If you're on the side of the Earth directly underneath the Moon, then the effective gravity feels about 0.00001% weaker, and if you're on the side of the Earth directly opposite the Moon, then the effective gravity feels about 0.00001% stronger.

Obviously this isn't a huge effect. But this little difference is still enough to cause the tides to flow in and out.

level 2
Particle Physics | High-Energy Physics6 points · 1 month ago

So the original Earth would have been more massive

Wasn't the impactor more massive than the Moon today?

level 3

Yeah. The proto-Earth and Theia (~10% of total mass if Mars-sized) became Earth, with about one percent of the total mass thrown into orbit and forming the moon, plus some amount would have escaped entirely.

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