Tidal energy, where does it come from?

This is another thread about free energy... (well more or less clarification)

ok so no doubt that everyone has witness tides (water) and most people will know that it is caused by the gravitation effects of the moon on earths water, and we get the cyclic tides because of the moons rotation around the earth.

Now the question is where does the energy form this movement of water come from because the amount of energy that is needed to move the amounts of water is incredible.

so it appears that the moon is generating this energy with a combination of its gravity and orbit... and in effect creating 'free energy'? because gravity is a natural force and apparently infinite.... am i right in assuming this?

Understand what i mean?

Mod Edit: Fixed spelling in title

[edit on 5/20/08 by FredT]

Gravity, it is very powerful stuff. Technically its where hydro power sources from as well.

yeah but first the water must be evaporated to get to the higher points... so the energy released from the falling water was once solar energy..

Mainer got it right.

Gravity is probably the most powerful force in the universe in terms of potential. After all, nothing can escape a black hole's gravitational pull.

If you have time, retype the Title of they post ENERGY is spelt wrong just in case people get confused.

reply to post by 44soulslayer

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yeah i understand its a powerful force but the question is... is it possible to harness it as free energy... just like the moon appears too.

Yeah sure, it is already underway in Maine and NYC.

They put turbines under water at tidal choke points. Like windmills but water passes through the fins.

reply to post by Mainer

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no i understand this... but the question was where does this energy come from... because there seems to be no input energy into the moon (eg. the suns input energy being hydrogen to helium fusion) but it is still able to output a great energy source... and i know you can say gravity but it is a combination of both gravity and the moons orbit (which is also a gravity related phenomena) that creates the movement of water and therefore energy.

So is this free energy or not?

It's quite simple. The tidal energy is taken from the earth's rotation. The earth has a tremendous amount of kinetic energy, as it has an unbelievably huge mass. The amount of tidal energy used up yearly is but a tiny billionth of the rotational kinetic energy of the earth. Despite this, though, if everything continues as normal, the earth will become tidally locked with the moon, just like the moon is tidally locked to the earth.

In the past couple billion years, the earth has slowed to about half it's original rotation speed.

Many bodies in the solar system have become tidally locked. (moons, mostly, but Pluto is locked to it's moon, and vice versa.) This is when the tidal forces have used up all the rotational kinetic energy in an orbiting body, and it now permanently faces the thing it's orbiting with one face. This happened to our moon long ago, and will eventually happen to the earth, unless it's destroyed first, or the moon drifts away.

It happened to the moon long ago, while the earth is still rotating at about half it's original speed because the earth is far, far more massive than the moon. The moon is one fourth the diameter of the earth, and a bit less dense, which works out to just 0.0123 times the mass of the earth. (just 1/80 the mass of the earth!) (it has a full 1/6th the earth's gravity at it's surface because of it's much smaller radius)

If the earth wasn't rotating, there would be no tides; it would just be slightly deformed towards and away from the moon.

It ain't free or infinite energy any more than solar or wind or hydroelectric power is. It will simply last far longer than man will probably be around. There's no reason not to use it; it's not going to slow the earth's rotation any faster (unlike some interesting proposals involving gyroscopes at the equator).

oh i see... so eventually the world will cease to spin..

now the question remains if energy cannot be created out of nothing then how did come to be?

Ok so can someone please tell me what Wave and Tidal energy are but using words that a child could understand

Wave, as in... the waves of the ocean. The energy that moves the waves across the sea, and the energy that controls the tides (hence the Tidal) of the sea as well.