Re: buoyancy puzzle (long!)

[Robert Cohen <Robert.Cohen@PO-BOX.ESU.EDU>]

> -----Original Message-----
> From: Carl E. Mungan [mailto:mungan@USNA.EDU]
> Sent: Wednesday, May 01, 2002 4:09 PM
>
> [snip]
> 2. This time I completely replace the water in the
> gap between the two blocks with rubber cement. I again let go. What
> happens? Under what circumstances (if any) would the two break apart?
>
> Let me remind you of the 3 proposed solutions:
>
> A. They can break apart. The likelihood of this happening depends on
> the depth of immersion of the blocks because the force between the
> blocks is purely tensile and has no compressive component.
>
> B. They cannot break apart. It is invalid to talk about a buoyant
> force on each block individually so there is no tendency for the
> blocks to fly apart.
>
> C. They can break apart. The likelihood of this happening only
> depends on the difference in densities of the two blocks and not on
> the depth of immersion. The physics is the same if we replace the
> glue with a bunch of strings.
>
> [snip]
>
> Who else would like to argue a case? Can anyone think of a simple,
> decisive experiment to settle the issue? Carl

Idealization 1: Replace the glue with strings.  This is option C.

Idealization 2: Replace the glue/blocks set-up with one where two cylinders
(one < d, one > d) are placed in a frictionless, massless tube with (your
choice of non-springy material) between the two cylinders.  This is option
B.

The question is: which idealization better reflects the performance of real
glue?  FWIW (not much), my vote is with idealization 1.

____________________________________________
Robert Cohen; rcohen@po-box.esu.edu; http://www.esu.edu/~bbq
Physics, East Stroudsburg Univ., E. Stroudsburg, PA 18301