Re: possible stiffness effect

[John Denker <jsd@MONMOUTH.COM>]

At 05:38 PM 2/7/00 -0500, Ludwik Kowalski wrote:
>  Subsequent student experiments
> showed that the measured speed (via single pulse and via
> standing waves) was 12% (+/- 5%) higher than what was
> expected on the basis v=sqr(T/mu)=sqr(15/0.086) which
> leads to 13.2 m/s (+/- 3%).

Can't say I'm surprised :-)

> Is the 12% difference due to stiffness or to something else?

1) A sensitive check would be to look at the spectrum.  That is, plot the
frequency of the Nth standing wave as a function of N.  In the absence of
stiffness, you expect the simple Pythagorean integer ratios.  Stiffness
will cause "stretched" intervals.

2) Another test would be to compare the following:
  2a) Clamp each end of the slinky to a board that fixes not only its
position (y) but also its direction (dy/dx).
  2b) Fasten each end to some sort of pivot (perhaps using short strings
like the bridle on a kite) so that y is fixed but dy/dx is not.

This will affect the lower-order standing waves more than the higher-order
ones.