Re: Orbital mechanics question (moon)
From: Brian Gaff (Briang1_at_blueyonder.co.uk)
Date: 10/06/04
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Date: Wed, 06 Oct 2004 09:59:13 GMT
"John Doe" <jdoe@doe.org> wrote in message news:416270D0.CA14AA49@doe.org...
> The moon literally moves oceans by creating tides which have a lot of
energy
> (and in fact some of it is converted to electricity with tidal power
dams).
>
> Does the gravitational pull of moon against the moving oceans result in
the
> moon actually losing kinetic energy (which would mean that its orbit would
> decay over time ?)
>
> If the moon's orbit does not in any way lose any energy even though it
moves
> oceans, where does the energy that creates the tides come from ?
>
> Or is this an example of a perpetual motion machine that never loses any
> energy ?
Well, my education may not have been to University standards, but I seem to
recall that the Moon is gradually getting further away from us, which is a
result of the interaction of its mass with other masses, in your case, our
oceans, and to some extent, the land as well. Its not exactly friction, but
it is obvious that some loss of energy has to occur. Higher orbits are
slower orbits of course, and presumably, as the moon recedes, the tidal
effect will too. The reason the effect on the Moon is so small is that, in
effect, the gearing of the work it is doing is huge, in that a lot of work
is done, but very slowly.
Remember, that the Earth is also rotating, and I'd expect this motion to
also be altered as the work gets done.
Of course, the Sun has an effect as well.
No figures from my addled brain, but I'm sure there is a tidal anorak about
with them at their fingertips.
What I want to know though is this.
If you take energy by moving mass from the moon, and it gets further away,
and you take energy out of a spacecraft in LEO by friction and it re enters,
where is the point where it, in effect crosses over?
:-)
Brian
-- Brian Gaff....Note, this account does not accept Bcc: email. graphics are great, but the blind can't hear them Email: briang1@blueyonder.co.uk ____________________________________________________________________________ __________________________________ --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.772 / Virus Database: 519 - Release Date: 01/10/2004
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