Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Have a Physics Question



Actually this person said "Got a physics Question." but I find that
locution objectionable -- It make one think of AOL's use of "You've Got
Mail" and bragging about it. Uggh!

This question is from a mature but undergrad physics major -- I wonder how
the list will comment.

I was doing a lab last week involving waves on a string. One end was looped
around a vibrating hook that generated the waves. The other end was draped
over a pulley and had a weight at the end. Your basic F vs. wavelength
setup. At a certain F, the pulley rotated counterclockwise ( if the wave
generator is on your right, and the pulley to the left). If you stopped the
pulley with your finger, it would start again when you took your finger off.
It rotated at constant speed, maybe 2 or 3 rev/sec. The professor in
attendance claimed to have never seen the phenomena in the 40 years he's
been there. My lecture professor can't figure it out. There's another
professor there who is supposed to be really good at mechanics and I haven't
heard if he has an explanation yet. I've seen this before, although I
can't offer any examples. I don't think the force comes specifically from
the string. I think it has everything to do with the vibration. I think
you would see the same thing if you had a wheel (or any round item) on an
axle that is vibrating, say a washer. It would have to fit tightly, but
allow for near-frictionless conditions. I know I've seen this before, but
since there seems to be no explanation for this by my professors here, I
wonder how it might be explained by others. I tried to look for a bulletin
board like the one you had me go to before, but I couldn't find it. I think
it would be as interesting, if not more, than the argument over the reason
why a wing works (low pressure lifting wing, or downthrusting of wind
pushing wing up). So, I thought I would go to someone who might explain
this phenomena. I look forward to hearing what you have to say.





Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.