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Re: [Phys-l] nifty question (solution)

On Fri, September 24, 2010 9:36:21 AM John Denker wrote:

For *anything* hanging in stable equilibrium, if I push on
it *anywhere*
-- the energy is unchanged to first order, for a push in
*any* direction ... by definition of equilibrium.
-- the energy goes up to second order, for a push in
*any* direction ... by definition of stability.

I think these statements should relate to potential energy only. For a
pendulum on a string in stable equilibrium, only potential (not kinetic!) energy
is unchanged to the first order for a push in any direction. Kinetic energy, and
thus the total mechanical energy may change already in the first order.


Moses Fayngold,
NJIT

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