Re: [Phys-l] Q from amplitude width?

[brian whatcott <betwys1@sbcglobal.net>]

On 4/25/2011 11:34 PM, Bernard Cleyet wrote:
> At 100Hz my LCR SRS meter displays ~ 200mH and Q ~ 0.3  at 10kHz the Q 
> rises to ~ 30, so I suppose, as  any coil will have a resonance from 
> the distributed capacitance.  (assuming the wire is copper and not 
> nichrome!)
>
> ~ 5.5 / 2Pi ~  0.88Hz.
>
>
> If you go to:

<http://www.cleyet.org/Pendula,%20Horological%20and%20Otherwise/Pendulum%20response%20to%20E 
<http://www.cleyet.org/Pendula,%20Horological%20and%20Otherwise/Pendulum%20response%20to%20E->M%20harmonic%20drive%20as%20a%20function%20of%20bob%20m/Pendulum%20response%20to%20EM%20harmonic%20drive.tiff>

/snip/

Going back to basics, it's interesting to assign an equivalent length to 
your pendulum, and supposing the mass is all in the bobs, assign a 
potential energy for the position where the bob reverses direction.
Your values for Q then provide a measure of the potential energy lost 
(as height) for each bob weight per cycle of free decay.

This then provides a figure for the actual power required to maintain 
that amplitude for that bob weight.

If the losses were all in the aero drag, then the maintaining power 
ought to be rather similar for various masses.    This is not the case 
for your numbers. One could assign this increased power requirement at 
increased mass  to increased aero drag (with mass) and/or increased 
suspension loss (with mass)

Brian W