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I wish I knew enough about physics to take a stab at figuring out how much energy we would need to remove from ocean tides to de-orbit the moon.
by philsnow 6y ago
I wish I knew enough about physics to take a stab at figuring out how much energy we would need to remove from ocean tides to de-orbit the moon.
- marcosdumay 6y agoI don't think you can increase the rate of extraction with a water power plant. Mining may do so, but I don't think you can do anything with the ocean (except for increasing or decreasing its volume) that will make a change, how small that may be.
- londons_explore 6y agoI think you're wrong. 1. If the water is fully frictionless, it will form a wave moving in phase with the moon, and extract no energy. 2. If the water is a solid, it will not move, and extract no energy. 1.5. If the water has the perfect viscosity/friction/resistance to flow, it will be 90 degrees phase away from the moon, and extract the most energy. The real moon is more like 1.1. Adding more resistance in the form of water turbines will get us closer to the 1.5 scenario, extract more energy, and cause the tides to stop sooner. Anything humans can build I suspect would be insignificant though...
- marcosdumay 6y agoThe main issue is that the water is interrupted. That means that friction or not, any movement will die off. So it already extracts nearly the most it can (the small difference being energy transmitted through land, the impact here is non-zero). That power plant is just making it die on it, instead of on land. (Anyway, the final configuration is not the Moon colliding with Earth, is it getting tidally locked.)
- DubiousPusher 6y agoIsn't the moon already tidally locked?
- marcosdumay 6y agoIts rotation is locked to its translation. Its translation isn't locked to Earth's rotation (that's why we have tides). It will eventually become, but I think the Sun will burn everything up earlier.
- DubiousPusher 6y agoOh, I didn't even realize that was possible. So the moon would only ever be visible from the same half of Earth?
- marcosdumay 6y agoSure they tend to get in sync, they are interacting, aren't they? Due to conservation of momentum, tides can't just change the Moon's orbit without affecting something else. That something else is Earth's rotation. And the only way to take energy out of the system while still conserving momentum is for the Moon to move into a higher orbit while the Earth rotation slows (because the Earth rotation is faster). That can lead to either the Moon being ejected from orbit or to its rotation being locked with the Earth day (that gets very long). Our current configuration leads to the later. But none of those will actually happen. The Earth tides from the Moon rotation are just not relevant enough for them locking on a Sun-like star lifetime.
- philsnow 6y agoIf we had immense pumps that could keep the tidal menisci whereever we want, say N degrees ahead/behind of the moon, my gut feeling is that keeping the closer meniscus 60 degrees behind would create the most 'drag'
- jay_kyburz 6y agoAlong the same lines, I've always wondered how much wind we need to capture before we start to change the weather.
- candiodari 6y agoWeather is chaotic, so the answer is simple: epsilon (any number, arbitrarily small, different from zero).
- omginternets 6y agoHe probably meant to say “climate”.
- tim333 6y agoIt's surprising to me that the moon is speeding up and getting further away from Earth. You might think the energy extracted to make tides would have the opposite effect.
- deleted 6y ago[deleted]
- Jabbles 6y agoThe moon is getting further away, but slowing down. https://en.wikipedia.org/wiki/Tidal_acceleration#Quantitative_description_of_the_Earth%E2%80%93Moon_case https://en.wikipedia.org/wiki/Tidal_acceleration#Quantitativ...
- Arnavion 6y agoTo get to a higher orbit ("further away"), you need to go faster than what you're going right now. Once you're in the higher orbit, you're going slower than what you were going at in the lower orbit.
- Arnavion 6y agoThe Earth is pulling the Moon along its orbit faster than the default speed of the orbit, by dragging the tides ahead of where they would normally be. So the Earth's rotational energy is translating into a higher orbital energy for the Moon.