🚀 go-pugleaf

ACTIVITY 8  floating objects

There was a statement on page 471 of the most recent issue of The Physics
Teacher (in the middle of the left column) which I quote. "If the buoyant
force acts at a point below the center of mass of the system, the system
is in unstable equilibrium." Do you agree? In my opinion the statement is
correct for some systems but incorrect for others. For example, a wooden
cylinder is vertically stable while floating in water, provided its diameter
is large in comparison with its height. A long and narrow cylinder, on the
other hand, is not vertically stable; it will "capsize". Show floating
cylinders to students and ask for explanations. Remind them that the law of
Archimedes is satisfied by all floating objects. That law, however, does not
deal with stability.

What I would like to know is HOW SHOULD THE CONDITION OF FLOATING STABILITY
BE FORMULATED TO COVER ALL POSSIBLE CASES? By the way, I like the source of
the quotation, the article by Marie Baehr. And I realize that the quoted
sentence was correct in her context; she was dealing with tall and narrow
objects. Many interesting demonstrations can be performed on the basis of her
publication. Unfortunately, the issue of tilted equilibrium, which preoccupied
me in ACTIVITY 1, was not addressed in the article. I am still trying to find
a way to theoretically predict the tilt angle of a container when all of its
parameters (shape, size, mass, the amount of inner water, etc.) are specified.
Suggestions will be appreciated.

      Ludwik Kowalski   Kowalski@apollo.montclair.edu  November 19, 1994