This is a piece I am still missing. Most of the other energy on earth comes from the sun in some form or another. I understand how that works and how solar energy gets stored. Then, we have nuclear energy. Got that as well.
Tidal energy falls into its own category as I understand. The moon’s gravity moves massive amounts of water all across the earth all day, every day. We know how to tap a tiny part of that but the tapping isn’t the key point. It seems that this system is doing massive amounts of work all the time.
Well, it’s all gravity and two objects that have a mutual gravitational attraction already have potential energy to start accelerating toward each other. Tidal flow may look impressive but it’s the merest rounding error of how much potential energy the Earth has in relation to the moon and (to a lesser extent) the sun. Picture how much kinetic energy (potential energy expended) the moon would have if it suddenly stopped in its orbit and splashed down in the mid-Pacific. Tides are trivial by comparison.
I don’t doubt your veracity but I don’t follow this. The tides are the result of the gravitational attraction between the water and the moon being higher for the water that faces the moon. The fact that the tides go in an out are a result of the rotation. That is, it takes two to tango. There would be no tides without the earth’s rotation or the moon’s orbit (set aside for a moment that the moon couldn’t be there if it weren’t in orbit), but neither would they be there without the gravitational pull.
When the Moon was young, presumably it spun at a faster rate than it does now, and therefore it exposed (almost) all of its surface to the Earth. The gravitational pull of the Earth caused tides on the Moon, but because the Moon is a solid body the tidal ‘bulge’ was small. The bulge also tended to get pushed “ahead” of the Earth’s position in the sky (from the Moon’s perspective) because the Moon was turning and did not immediately ‘snap back’ once the Earth wasn’t overhead. The Earth’s pull on this tiny bulge of Moon tended to slow the Moon’s rotation down, to the point that the Moon now presents only one side to the Earth (give or take).
The Moon is doing the same thing to the Earth - it pulls up a tidal bulge on Earth, which ‘leads’ the Moon a bit. The Moon’s pull on this off-axis bulge tends to slow down the Earth’s rotation over time. Meanwhile, the Earth bulge adds a bit of off-axis pull to the Moon and slowly but persistently boosts it into a higher orbit. The end result over time is that the Moon and Earth become tidally locked to each other, with the Moon in a much higher orbit, and the each presenting only one face to the other.
Overall, though, the angular momentum of the whole system is preserved, except for the energy that is radiated away as heat because of the frictional heating of all that flexing rock and water. An explanation with diagrams is here: Gravity Applications
There would still be a tidal bulge; the effects of gravity wouldn’t go away. But remember that gravity is NOT a form of energy, it is merely a transfer mechanism in the same way that magnetism is.
Oh, I see where I’ve managed to confuse you. Yes, the tidal bulge is caused by the difference in gravity on opposite sides of the Earth, but in order to extract any useful energy from it, there must be rotation. As I said, gravity isn’t a form of energy, but you can use it to get energy from one place to another. The same is true of an electric generator; the rotating magnets induce an electric current in a coil of wire, but the energy doesn’t come from the magnetism, it comes from the rotation.
I think you have it backward, actually. If Earth was to suddenly stop its own rotation, the moon in its orbit would still have a tendency to cause tides as its gravity causes the Earth’s surface to deform slightly. Friction from this would start the Earth rotating again, albeit very slowly. Its not the rotation of Earth that causes tides, but the gravity of the moon in combination with the rotation of Earth, though I admit at this point we’re getting pretty chicken-and-egg.
You misunderstand. I’m not talking about the cause of tides, I’m talking about the source of so-called tidal energy. That source is ultimately rotation, not gravitation.
No, you misunderstand that without gravitation, the entire idea of tides is moot and the tides can exist even without rotation, given the revolution of an orbiting body.
I’m willing to concede, however, that this comes down to how certain terms are defined.
No, I understand that completely. To go back to my previous analogy, generators won’t work without magnets in much the same way that tidal energy can’t be extracted without the Moon’s gravity. But, neither the Moon’s gravity nor the magnetic field are sources of energy. That is the only point I am making here.
If your definitions allow you to call gravity a form of energy, then your definitions are wrong.
Actually, I was trying to be polite and avoid calling you completely out to lunch on this subject, but so be it.
The electromagnetic analogies are completely misplaced, incidentally.
The source of this energy is arguably whatever supernova exploded to create the nebula from which our solar system gradually condensed into its current form, including a rocky planet that got hit with something massive, creating a rocky moon and setting up an orbital system that has been fairly stable for some five billion years so far, graaaadually losing its energy to waste heat.
No, they’re not. Gravity and electromagnetism are both fundamental forces. A force is not energy, it’s a medium for transferring energy from one place (or thing) to another. I’m not sure why you can’t understand that, but perhaps I’m explaining it poorly.
Yes, you can trace the source of tidal (and indeed, all other forms of) energy back to the Big Bang, but that’s not really germane to the subject.
You’ve never heard of gravitational potential energy? You can’t seriously be saying that there is no energy stored up in the moon by virtue of it orbiting the earth.
Clearly the rotational energy stored in each body is affected by the tide, but if neither body were rotating, rotational energy would be zero, and the tides would still exist.
Gravitational energy is not yet energy. It is the potential for a force to act on an object to give it energy, or reduce energy. If you are motionless in the middle of a ladder, you have this gravitational potential energy reletive to the ground. There’s no energy there until you jump off of the ladder and allow the force of gravity to pull you down. Conversely, if you decide to climb higher, you must use energy to overcome the work done to you by gravity.
(Kinetic) Energy = 1/2 m v^2
Work = force . distance
If you allow gravity (the force) to act on you over a distance it will do work on you, possibly increasing your speed (if you are going with gravity, possibly acting against your motion if you go opposite the tug of gravity).
Potential Gravitational Energy is a convenient way to avoid doing work calculations, but is not the “full” truth. It’s not a “real” energy in the same way that the Coriolis force is not a “real” force. They are merely physics shortcuts.
Tides exist because Earth is spinning under (or around) two bodies: Luna and Sol. If Earth, Luna and Sol were in lock-step, with rotations and revolutions matched, there would be tidal bulges, but no tides.
For comparison, Pluto and Charon rotate in sync with each other. (If you stand on one side of Pluto, you will either a. always see Charon in the same place, or b. never see it.) Thus, there are no tides, merely tidal bulges.