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Re: dropped slinky



John S. Denker wrote:

John Mallinckrodt wrote:

> I've put an animation built with Interactive Physics online
> at http://www.csupomona.edu/~ajm/special/slinky_drop.mov

That movie displays what one might call non-ideal
behavior.

In particular, the movie shows 9 red beads that
come together and _stick_. That implies there must
be some sort of dissipation mechanism; otherwise
the beads wouldn't stick. I'm not sure exactly
what sort of dissipation is being assumed, or why.
No such dissipation was specified in the original
statement of the problem.

I was merely trying to model what a real slinky does. When you drop
a real slinky in this fashion, its coils come together in collisions
that are overwhelmingly inelastic. Perhaps not 100% but darn close.
The mechanism is the same as that of any inelastic collision between
macroscopic objects with oodles of internal degrees of freedom.

It is edificational to consider another brand of
slinky, i.e. one that doesn't have this "sticky"
property. The slinky is, after all, just a medium
for the propagation of waves, and most media do
not have the property that they compress once and
get stuck in the compressed state. A slinky does
weird things when the turns slap together, but it
doesn't just stick.

I'd suggest doing the experiment. They pretty much just stick.

--
John Mallinckrodt mailto:ajm@csupomona.edu
Cal Poly Pomona http://www.csupomona.edu/~ajm

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