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Re: [Phys-l] Discrepant amplitude measurement



On 08/03/2011 01:47 PM, Bernard Cleyet wrote:
The horological community principally uses two methods to find the
amplitude of a pendulum -- one is an obvious use of the work energy
theorem. i.e. measure the speed at the equilibrium position

Energy is not amplitude, and amplitude is not energy. Each is
related to the other by fairly simple formulas, but "related
to" is not the same as "same as".

the other the time the pendulum is "beyond" the photogate

Here we go again: time beyond the photogate is not amplitude,
or vice versa. Each is related to the other by some weird
nonlinear formulas.

===========

If you want to measure the amplitude, measure the amplitude
... or measure something else and convert. If the methods
don't agree, you're not doing the conversions right ... or
not doing the raw measurements right.

If I were instrumenting a clock, I'd start by putting a Gray-
coded optical encoder on it (not just a single photogate).