[Phys-L] Re: A "simple" physics problem?

[John Mallinckrodt <ajm@CSUPOMONA.EDU>]

Previously I wrote:

> For the most part, AS the ice cube melts, NOTHING happens to the
> level of the water.  The melted ice, which previously DISPLACED its
> weight in water simply BECOMES its weight in water.  But, at some
> particular instant, enough ice has melted so that the lead shot
> suddenly drops from the ice cube.  The remaining ice, relieved of its
> weighty burden, quickly pops upward as a result of the (now) excess
> buoyant force.  The water level drops as surrounding water rushes in
> to fill the void.

However ...

In order to float the lead shot, the ice cube must have a certain
minimum overall volume.  As the ice cube melts, the water level
remains constant but the ice floats lower and lower in the water
(i.e., the submerged percentage increases.)  If the ice cube melts to
less than the minimum required volume before releasing the shot, it
will sink to the bottom.  At that point further melting will
continuously lower the level of the water.

At some point the remaining ice may still detach from the lead shot
and pop to the surface resulting in a sudden drop in the water level.
After that the level will remain constant as the now floating ice
finishes melting.

John Mallinckrodt
Cal Poly Pomona
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