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Rotational Speed and Orbital Parameters
Name: Brian
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
If we could change the rotational speed of the moon, would
this momentum change necessarily change its orbital parameters?
Replies:
Brian,
In the short run, giving the Moon a spin would not affect its orbit around the Earth.
In the long run, the energy of that spin might gradually be
transferred to its orbital motion and consumed,
by means of tidal deformation of the moon.
Personally I do not how much coupling to tidal stresses happens
in a cold, all-solid body like the Moon.
The degree of coupling could be much less than that of largely-fluid Earth
if the moon is infinitely rigid or perfectly elastic,
or it could be much greater
if there is any yield or crumbly sliding deformation within the body.
Perhaps you have heard:
the spin energy of the Earth has been partly transferred to moon's orbit
over the time since the Moon was created, driving the Moon farther out
and slowing the Earth's day/night cycle.
This is the type of coupling I am referring to above.
Jim Swenson
Brian
If you are speaking about the rotational speed of the moon on its axis,
Then no, that will not affect its orbital parameters.
If you change the speed of the moon's orbit around the earth, the moon will
move out to a more distant orbit until its velocity vector parallel to the
surface of the earth equals its velocity Vector that points toward the
center of the earth.
Sincere regards,
Mike Stewart
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Update: June 2012
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