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this post was submitted on 28 Oct 2026
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This raises an interesting question in my mind, does tidal power make the earth get closer to the moon? Because if you got all the energy out of it, then the water wouldn't move, so I guess it's the same as gravitational potential in that sense, but I guess it's removing it, so less gravitational potential means either less mass (not the case) or less distance.
The opposite happens. Tidal energy is what causes the moon to drift farther away from the earth, as the moon loses angular velocity.
But does harvesting it make it go faster or slower away?
If you mean harvesting tidal energy, the effect on the moon would be minimal. The loss of angular momentum the moon experiences is due to the mass of the earth’s waters. I could not imagine anything humans could build that could extract enough tidal energy that it would disrupt the moon without utterly destroying the environment at the same time (by way of nullifying tides somehow). In fact, to harness tidal energy, one way would be to use underwater turbines. They would have an immediate effect to the local environment but a negligible amount to the moon itself.
I know its minimal, I'm not saying it's a concern, I'm just saying if we are harvesting it, doesn't that mean it's pulling us closer to it? It's not magically free energy (in the physics sense), so what else could it be other than converting the potential gravitational energy between the earth and moon into something else?
see my other reply in this thread
basically it doesn't move the moon closer, but it makes the Earth rotate slower. that's where the energy comes from.
basically the tides transfer angular momentum from the Earth to the moon.
actually, the moon gains angular momentum from the tidal movement that it causes, and that's what makes it move further away. the reason is that it takes Earth about 1 day to rotate once around its axis, but it takes the moon 28 days to rotate once around Earth's axis. so Earth has a higher angular velocity, and the tidal movement tries to reduce that difference to make the two tidally locked eventually. ironically, this process transfers angular momentum to the moon (to speed it up), which makes it move further away and thus the angular velocity actually decreases. yeah, orbital mechanics is weird.
(btw this is not a joke. it's really that way, difficult to comprehend i know).