Re: Question -> Re: dropped slinky

[Bob LaMontagne <rlamont@POSTOFFICE.PROVIDENCE.EDU>]

Tina Fanatic wrote:

> Hi all
> I am working on a take home test for my calculus physics students.  W=
> e covered simple harmonic motion and conservation of energy.
>
> I think the dropped slinky problem would make a nice extra credit pro=
> blem but am unsure as to how to set it up as a question for them.
>
> Suggestions?
> Tina

The inverse of the slinky problem is a classic and is doable as extra credit in an
exam (I've used this myself at times.) It's the problem of a wave pulse moving up a
hanging rope. Here the motion starts at the bottom at zero speed (instead of the
infinity at the top of the slinky) and the speed increases as the pulse travels up the
rope because of the increase in tension due to the increased weight of rope hanging
below each segment.

As a question, you could simply ask how the speed of the pulse varies. As a problem,
you could set up a standing wave by wiggling the bottom and ask how the distance
between nodes (or wavelength) varies as a function of distance from the bottom.

This is great as a demonstration also. Using a long flexible spring one can see the
wavelengths on the standing wave going to zero at the bottom. Thanks to the people who
have analyzed the slinky on this list, you could extend the thinking to the slinky
demonstration.

Bob at PC

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