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Re: Bar magnets

The question has been asked about the Coulomb balance and whether this is
always used with repelling charges.

I believe the answer to this is yes. We have the Pasco Coulomb Balance and
get nice results with it. Like the original Coulomb balance, this is a
torsion balance. Students ask (each year) if they can measure attraction
rather than repulsion. I say, "Sure, give it a try." Of course no one is
successful. As far as I can tell (both theoretically and experimentally) it
is not doable. If the torsion wire is stiff enough to allow a stable
equilibrium for attractive forces, then it is not sensitive enough to yield
a meaningful measurement. If it is weak enough to allow sufficient
sensitivity for a meaningful measurement, you simply cannot attain a stable

I have had quite a few students try.

Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail
Bluffton College
280 West College Avenue
Bluffton, OH 45817