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It could be argued that relative to a fixed point on the stationary
coin, the moving coin only rotates once. How many times the coin rotates would seem to depend on the frame of referrence of the observer.
So, does the moon rotate about its own axis?
A Foucault pendulum can be used to detect the inertial effects caused by the rotation of astronomical bodies.
If this pendulum were placed on the moon it would indicate that the moon does indeed rotate as it circles the earth.
However, this does not put an end to the argument. If the moon did not rotate, but instead the universe rotated about the moon, the pendulum would still act in exactly the same way. General realtivity shows that
the gravity fields created by a rotating universe about a non-rotating moon would produce the same effects as the inertia fields which are generated if the moon rotates in a fixed universe.
It would therefore seem that in order to get to grips with this problem one needs to think in terms of relative motion.
CONFUSED?
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