Re: physical pendulums

[Herbert H Gottlieb <herbgottlieb@JUNO.COM>]

On Wed, 22 Sep 1999 19:30:53 -0700 fred brace <fredb@TELEPORT.COM>
writes:
> I am using a set of physical science lab materials on the pendulum.
> One of  the activities asks the students to get a washer, a bolt and a
long
> wooden  dowel to swing with the same frequency. It says that if the
center
> of  masses line up, then the pendulums will have the same frequency. Is

> this true?

This is almost true, but not quite true.  For a uniform wooden dowel, the
center of mass is at
the center of the dowel.  It's "center of oscillation" is located at
distance equal
to 2/3 of its length , measured from its point of suspension.   Thus a
simple pendulum
consisting of a uniform steel washer at the end of a string of negligible
mass
would have the same frequency as the swinging wooden dowel if the length
of the
simple pendulum is 2/3 as long as the dowel.  This is explained in detail
in most of the
popular physics books for introductory physics.

Herb Gottlieb from New York City
(Where Professor Zemansky of our City College did a great job
explaining this in his College and University  Physics testbooks).