Re: Does motion affect the operation of clocks or not ?

a student wrote:
pendulum clocks behave
quite differently to atomic clocks under motion (try dropping a
pendulum clock - it won't work at all in freefall).

This is a misnomer, based on differences in word meanings between everyday life and physics. In physics, a "pendulum clock" consists of the pendulum, its pivot, AND THE EARTH (plus a counting mechanism). Dropping just the pendulum and its pivot is BREAKING the clock, because its behavior AS A CLOCK depends on a fixed relationship among all its parts. So it's no surprise that it behaves differently from other clocks which are not broken.

If you could keep the pivot fixed to the earth, and "drop" the whole shebang in such a way that the gravitational force on the pendulum is not significantly affected, then this clock would not be affected by dropping it. Indeed, this occurs every day as the earth orbits the sun.

NOTE: I mean the clock itself is not affected. In another post I'll discuss the difference between affecting THE CLOCK and affecting OBSERVATIONS of a clock -- that is the real crux of the original post in this thread.


Tom Roberts

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