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Re: Newton's Second Law Lab



Note that Tom McCarthy's solution with an Atwood machine requires the same
type of simple analysis I described in my first post, or else you still end
up with analysis of two bodies that can be difficult for some students. I
consider the Atwood machine and the air-track/falling mass experiment to be
the very same experiment. In fact, I call the air-track experiment a
"horizontal Atwood machine" (even though it is only half horizontal).

One good thing about the Atwood version is it does not require an air track,
and the good pulleys indeed work well. One bad thing is the movement is not
as constrained as an air track glider. So it can be problematic to keep the
"flag" or "picket fence" from swinging or rotating as it goes through the
photo-gate.


Michael D. Edmiston, Ph.D. Phone/voice-mail: 419-358-3270
Professor of Chemistry & Physics FAX: 419-358-3323
Chairman, Science Department E-Mail edmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817

Tom McCarthy said:

It is very difficult to stage a constant force and investigate the simple F
= ma. What I have done instead of the air track is to use an Atwood machine
using the very slick and light pulleys from PASCO. By keeping the mass
difference the same (F = constant), the acceleration and mass can be
investigated with a high degree of accuracy, especially if a picket fence is
used. Also, when the mass difference is zero, they can see, first-hand,
Newton's first law at work, especially if you make the Atwood machine very
long. I do it off a balcony so there is about a 7 m drop zone. Also, by
keeping the mass constant, force and acceleration can be investigated.