Talk:Tidal power
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Let's see some diagrams of machines that harness tidal power, eh?
Just wondering: the tides are caused by the moon, and the moon will never stop orbiting the earth, right? So does that make tidal power perpetual motion, or am I overlooking something?
A: The tides slow the Earth's rotation down. So the source of the tidal power will be exhausted at the precise moment when the rotation speeds of the Earth around its axis and the moon around the Earth will coincide. Then the day should last more that a month now:). Harnessing the tidal power should not, IMHO, change anything in this natural process - just some part of the energy that now is dissipated as heat will be converted to electricity or whatever.
Deceleration of the earths/moons orbit
Why would the earth and moon decelerate in a vacum? Surely after 4 billion years of decellerating would cause all sorts of problems! As the earth is decellerating in one direction, surely the tides would 'sit' on certain coast.
I was taught that the gravity due to the sun and moon on a side of the earth at any one time causes the sea to swell (cuasing the earth to appear elliptical), hence creating two tides per 24 hours. If this is so then we are not taking energy out of the movement of the moon and sun, but out of these movements in the sea.
A: The earth and moon do theoretically slow down as they are moving in a constantly changing path. However you a correct, the decelleration of the earth has very little effect on the tides, more dominant forces include the Coriolis effect, energy form the sun, tidal resonance, funneling, atmospheric pressure, high & low pressure reigons...
To conclude to say that the root of tidal motion is due to the decelleration of the Earth and the Moons orbit is misleading - in some schools it would be termed "wrong".
Tidal harness
Someone might want to merge tidal harness with this article or visa versa as they appear to be talking about the same thing.--GD 10:28, 26 Sep 2004 (UTC)
So the energy is only "considered inexhaustible within a human timeframe". We mean, then, that it isn't really inexhaustible, just "considered" so?. The "human timeframe" part: do we mean it will run out in a century or two or something? Weaselling for weaselling's sake. Couldn't this be stated with more conviction? --Wetman 11:41, 24 Oct 2004 (UTC)
It's "more than enough energy" or more energy than we can possibly hope to convert using our lousy tidal power barrages. --Evgeni Sergeev 11:45, 24 Oct 2004 (UTC)
No, it isn't really inexaustible. If we look from the universe's point of view, energy is just moving around, changing forms, not being created, nor destroyed. When we use non-renewable energy, like fossil fuels, we extract energy at a much faster rate than it is being stored. This means our supply will run out eventualy, but quite soon, actually. When we extract energy from Sun's rays, we know that the Sun will be there whether we extract this energy or not. The Sun is independent of devices to get the energy -- it will radiate the same amount of energy whether or not we convert some of it into electricity. It will run out of energy too, but not due to our activities. Now, tidal power is different to the Sun, as when we are building a tidal barrage, we are increasing the friction (well, not quite, we are increasing the impedance) of water movement around the Earth. Thus we are contributing to the Earth's rotation slowing down. Yet if we perform rigorous calculations, using mass of the Earth, its angular velocity and the maximum amount of energy we are taking away, we will get a contribution of a very small change in angular velocity in a very large number of years. This is much more like the Sun example, than the fossil fuels example, so we call this renewable energy.
Now, it is "considered" inexaustible within a human timeframe because we don't know how long the human timeframe will last for. Personally I believe that once we invent decent AI, we will spread out over the galaxy, and only a huge catastrophy will stop us then. This is probably fantasy to you, but I'd like to see a proof if you insist that the human timeframe is short. --130.95.128.58 01:35, 26 Oct 2004 (UTC)