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Lunar tides churn earths oceans and soils. The resulting fricitional heat energy accumulates in earth or radiates to the space. Conversely, earths tidal force on the moon accumulates heat energy in moon.
These energies come from, and diminish, the kinetic energy of moons revolution around the earth. The diminished kinetic energy of moon results in the reduction of the radial distance of moons orbit around the earth.
As this process has been going on for billions of years, from the time of moons formation until now, the orbital distance of moon must have significantly reduced.
1) What is the name of this phenomenon?
2) What is the percentage reduction of the average distance of moon-to-earth (say) per million years?
3) When will moon fall on earth due to this phenomenon?
- Mehran (age 54)
Mehran- You've left out one other energy source for the problem, the
Earth's rotational energy. The astronomers say that actually the Moon
has been getting FARTHER from the Earth, so the net kinetic plus
gravitational potential of that part of the system is going UP, even as
tides heat the Earth. The source of that energy is the earth's
rotation, which is slowing down. When you think of it, the
almost-twice-daily changes in the tides must be more driven by the
Earth's daily spin than by the Moon's monthly rotation, so it's not
surprising that it's the Earth's spin that's losing energy. Then if you
remember that angular momentum must be conserved, you see that the lost
spin angular momentum has to go somewhere- and that's to the Moon
orbit. The direction of the orbit is such that its absolute angular
momentum increases, so that the orbit size increases.
As for how quickly all this is happening, a quick Google search turned up a reference
)that claims that the day has lengthened by about an hour in the last
240 million years, and that the Moon is getting some 3.8 meters farther
away each century. The phrase this source uses for the process is
(republished on 07/19/06)
Follow-up on this answer.