Re: Will the Moon Crash Into Earth?

On Feb 8, 10:31 pm, Jo Schaper <jospamnotschaper34@5socket78dot9net>
wrote:
effac...@xxxxxxxxxxx wrote:
I asked a science prof if the moon will eventually move away or into
the earth.

He said neither, it will remain revolving the earth for eternity.

Obviously after this insulting response I stopped taking him too
serious.

Well, barring a collision with an asteroid, the moon probably will
continue moving away (as it is currently by a few cm a year.) It likely
will remain in orbit at some distance, until both it and earth are
crisped to cinders by the expanding sun, a couple of billion years in
the future. A couple of billion years is close enough to an eternity for
me.

If earth and the moon were truly solid (elastic) bodies, then the moon
would stay at the same nominal distance until disturbed by something.
This is due to Conservation of Angular Momentum and Conservation of
Energy. HOWEVER, neither the earth or moon are truly elastic. The
earth has tides due to the moon and the moon has "tides" due to
earth. Thus some of the energy associated with the moons orbiting
earth turns into heat in the tides. This means it loses energy.
Kinetic energy = 1/2 I w^2 where I is the moment of inertia and w is
angular frequency of rotation ( I know, this is really simplified).
So if kinetic energy goes down, so does w. If w goes down, the radius
of the orbit INCREASES. Due to tidal losses, the moons orbit
increases about an inch each year. Apparently, a billion years ago,
it was closer, roughly a billion inches or 100 million feet or about
16000 miles closer.

.

Relevant Pages

  • Re: Lunar Space Elevator simply isnt for everyone
    ... As to an LL-1 based sizable asteroid tethered to the Moon, ... You do realize that a millionth of the surface area of mother Earth ... About energy, uh, there is a lot of recycling to be done. ...
    (sci.space.policy)
  • Re: Temperature on global warming turned up
    ... Global Warming is for real, and it's real in more ways than one. ... of the vast amount of required energy, ... obtained moon, which isn't discounting the 10% impact as caused by ... all departed this Earth and let nature and the laws of physics take its ...
    (sci.space.policy)
  • Re: USA urges scientists to block out sun
    ... our's to deal with as of the last ice age this planet will ever see. ... Take away our moon and Earth gets cold. ... it still has our polluted and energy raped ...
    (sci.space.policy)
  • Re: Temperature on global warming turned up
    ... if we all departed Earth and let ... that pesky moon of ours, ice age trapped methanes and CO2 will in fact ... energy into our environment by way of tidal forces, ... planetoid, as our solar shade instead of being a pesky moon. ...
    (sci.space.policy)
  • Re: Noethers Theorems (1918) in English translation
    ... >>momentum is from the Earth to the Moon. ... There is a net energy ... transfers energy up (rotation rate of earth> rotation rate of moon, ...
    (sci.physics.relativity)