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Re: The Capacitor problem - once more



At 09:23 6/3/99 -0400, Michael Edmiston wrote:
I disagree with Jack Uretsky's analysis that the person connecting the
capacitors absorbs the energy. In his experimental description he may
be correct, but he has changed the experiment drastically.

I think my spring pendulum analogy can help us here.

In the original case, simply connecting the two charged capacitors
together is like letting loose of a stretched spring pendulum. The
spring pendulum either oscillates forever (no friction) or dissipates
kinetic energy into thermal energy over some period of time. Likewise
the suddenly-connected capacitors oscillate forever (E-energy to
B-energy and vice-versa) or else energy is radiated via some
combination of thermal energy or as E&M waves.

The process Jack describes is not the same. Rather, his process is
like slowly letting go of the spring pendulum. Rather than simply
letting go, keep holding onto the spring-pendulum mass and move it
toward equilibrium, and only let go once it is at equilibrium. In this
case the person has "absorbed" all the energy that had been stored in
the spring. There is no oscillation and there is no generation of
thermal energy (other than in the person)....

Michael D. Edmiston

The physicist's strength in simplifying and idealizing, can be his
Achilles heel, if he moves from a (realistic) physical picture of a
pendulum losing a little energy each swing, to an (idealized) picture
of a pendulum being brought to rest so gradually that no energy is lost
thermally. This is the physicist's favorite idealization:
"In the limit..."

So to differ with Michael, there is always (practically) some energy
lost thermally to air turbulence etc. in setting a pendulum still.

brian whatcott <inet@intellisys.net>
Altus OK