Re: [Phys-L] adiabatic invariance confusion

[brian whatcott <betwys1@sbcglobal.net>]

It seems fanciful to suppose that a fixed solenoid interacting with a 
swinging button magnet
models a force due to gravity at all accurately. Supposing the solenoid 
imposed an extremely strong  magnetic field, the button magnet swinging 
in its vicinity would likely be immediately captured which I think you 
are equating to a high value of g. It seems to me that the force imposed 
upon the pendulum represents work done and so claiming adiabasis seems  
problematical.
Perhaps a very slow change in effective pendulum length - using pendulum 
bob or pivot point displacement might meet your needs better?


Brian Whatcott    Altus OK

On 2/28/2014 1:47 AM, Bernard Cleyet wrote:
> Showing an adiabatic invariance with a macroscopic harmonic oscillator is v. difficult, because of dissipation.  For another reason I’ve been changing the effective g of an E-M clock driven pendulum.  The magnet attached to the bottom of the bob completes the clock drive and serves to change the effective g using a solenoid waxed beneath the sense and drive coils of the Fedchenko type drive.  After many trials, I thought, perhaps a driven pendulum WRT adiabatic invariance would be the same as a dissipation-less pendulum.  So I tried changing the “g” using an RC supply to the solenoid (L ~ 190 mH)  The measured TC is ~ 93s   (R ~ 2K Ohm; C ~ 16K microFd calc’d 32s).  Nada!  Tho the g increase is ~ 35% (TC ~ 96s and the period is ~ 1s)  By a stroke of luck I thought, well, how about the extreme of my previous trials (TC < 1s!).  Wow!  The product Omega * Amplitude is the same once equilibrium obtained.   (W/ and W/O the added g  within ~ 1/2%)  While the ”supposedly" adiabatic trial has a difference of ~ 5%
>
> “What gives?”
>
> bc theory, etc. declined.
> _______________________________________________
> Forum for Physics Educators
> Phys-l@phys-l.org
> http://www.phys-l.org/mailman/listinfo/phys-l