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| quote: | Originally posted by DigiNut
It's called an orbit.
Let's hypothetically say that your "theory" were true - if that were the case, it would also be true for electrons orbiting atoms, and every atom in the universe would eventually collapse on itself. And considering their size, they'd collapse on themselves in an infinitessimal fraction of a second.
It should therefore be pretty easy to see why your hypothesis can't possibly be correct.
Tidal energy is based on a principle similar to the centrifugal/centripetal force from revolving motion in classic mechanics. That force does not slow down the revolutions or even affect the motion at all. It is in fact a "side-effect" of the motion itself - since the revolution requires a constant acceleration (and thus a force which is constant in magnitude), the aforementioned forces are in opposition to the accelerative force. Everything balances out - no energy is (under ideal conditions, neglecting air resistance and such) lost or converted in that process.
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Everything balances out under ideal circumstances only. When the moon (an external force in the Earth-water system) reorders the gravitational energy of the water through its gravity, it doesn't gain or lose any energy because the total gravitational energy in the water is constant. The force of the moon, as it revolves, tugs on the Earth, but because the moon is orbiting, and the Earth is spinning, all of these forces cancel and the net acceleration of the water is zero with respect to the Earth-moon system.
The problem is when you let the water fall at high tide (as in a tidal generating station), for a moment, the Earth is accelerated upward (in the direction of the water). Until the water lands, decellerating the Earth to its prior velocity. The system then loses energy. However, when the water rises back up, the system regains its energy. It's like a person jumping up and down. While he or she moving upwards, the Earth is moving downwards, and vice versa. The net displacement of both is zero at the end though.
The situation is different though when the rising force is external and the falling force is internal. In this case, the moon loses energy when the water rises, and the Earth loses energy when the water falls. Consider the following example:
A <-moon (in orbit)
B <-person
C <-planet
Suppose the person fires a grappling hook at the moon and pulls himself upwards a few stories onto a building. Then he jumps off and lands on the surface of the planet again. During the first part, he gets gravitational energy from the moon, and during the second part, he steps off the building and his gravitational energy is essentially converted into heating the planet up and making noise.
What you said is all correct... perhaps you didn't quite understand what I meant by tidal energy. I'm talking about tidal generating stations. They have a big empty pit that is above the low tide level but above the high tide level. Above that are some turbines... there are floodgates above and below the pit. During low tide, gate #2 is open so all the water in the pit is drained out. Then the gates are closed... when high tide comes, floodgate #1 is opened, the water flows in, turns the turbines, and makes power. When the reservoir is filled up, floodgate #1 is closed again and the process repeats itself.
--high tide--------------------
|===(floodgate 1)===|
|*******************|
|******turbines*****|
|*******************|
|...................|
|...................|
|===(floodgate 2)===|
---low tide------------------
If I'm wrong, could you please explain to me where this energy comes from?
___________________
I am nobody. Nobody is perfect. Therefore I am perfect.
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