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Re: Periodic motion vs. oscillation



Further reflection on this, induced by the responses of others
convinces me that oscillatory motion is in the eye of the beholder,
and the following example comes to mind:

Consider the moon's orbit. If we sit on the earth and look at it, it
appears to be orbiting the earth, and whether is it oscillating in
its orbit I guess depends on whether you want to consider its
eccentricity as important.

On the other hand, look at it from the perspective of someone at rest
relative to the sun. From that POV, the moon is in orbit about the
sun (a calculation can show that the moon's orbit is *always* concave
toward the sun, even when it is between the earth and the sun), with
the earth's gravitational perturbation providing an oscillatory
motion between it's two extreme positions relative to the sun.

Hugh
--

Hugh Haskell
<mailto:haskell@ncssm.edu>
<mailto:hhaskell@mindspring.com>

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