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Re: Pendulum acceleration



Tim,

Use a liquid-filled accelerometer of the PSSC variety which is mounted by
two strings that will remain parallel as the unit swings as a pendulum.
Notice that the accelerometer reads zero at the bottom and is a max
(towards the equilibrium position) at each extreme of the swing. The
accelerometer remains horizontal at all times. Then bring the (bifilar) two
strings together at the support. Notice that now the accelerometer reads
zero at all points of the swing with the reading being taken tangent to the
path. A real classroom crowd-pleaser. This is much easier to construct that
making a curved air track with an accelerometer on the glider (as was
actually demonstrated for me by the inventor of the popular form of air
track, John Stull).

Tom Ford


At 07:29 AM 10/24/01 -0400, you wrote:
In other words, the NET FORCE, and thus the acceleration, is
zero at the bottom and non-zero at an angle, large or small.

How can this be? Clearly it is moving the fastest at the
bottom and an instant later it must be moving slower.
This is a change in velocity - this is an acceleration. To
have an acceleration, a force must be present. Or am I
completely wrong of my understanding of motion?

Tim O'Donnell
Instructor of Physics and Chemistry
Celina High School
715 East Wayne Street
Celina, Ohio 45822
(419) 586-8300 Ext 1200 or 1201
odonnt@celina.k12.oh.us

"Chance only favors the prepared mind." - Louis Pasteur