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Re: Inertial vs gravitational mass



Cliff,
Remember the derivation of the period of the pendulum equation.
F = m(inertial)a = m(gravitational) g sin(Theta)
The final equation has no mass terms because you assumed that the inertial
mass that is accelerating is equal to the mass in the gravitational force
term. Newton made a hollow pendulum bob and filled it with various
materials to see if it was really independent of the material used. If the
inertial mass and the gravitational mass varied with different substances,
then the two types of mass were not equivalent! The equation given in the
texts assumes this equivalence. Newton was an amazingly insightful man. As
Einstein said Newton was more aware of the difficulties with his
assumptions then those of us who followed him!

Gary


At 09:42 PM 1/22/03 -0600, you wrote:
> "Again I am not sure what you mean by finding inertial mass via pendulum
> period. A pendulum period would not reveal any information about inertial
> mass."
>
>
> I beg your pardon, please explain.

Perhaps the word pendulum was used in a way that I am not familiar. The
pendulums with which I am familiar do not change period when the bob mass is
changed but rather when the pendulum length is changed.

Cliff Parker