Date: Wed, 27 Apr 2005 09:15:01 -0600

Author: Jerry DiMarco

Subject: contact vs non-contact forces


A visiting lecturer here recently used a different demo to introduce
the topic of electrostatics. A nickel was balanced on its edge, then a
wooden match was balanced on top of it. An upside down glass was put over
that, and another nickel was balanced on edge on top of the glass. The
students were then challenged to come up with a way of knocking the match
off the nickel without touching anything or knocking either of the nickels
over. What they were supposed to realize is that static electricity could
be used to pull the match off the nickel without affecting anything
else. Eventually the instructor used a charged rod near the glass to pull
the match off.
In the process of trying to add this demo to our collection, I
noticed there doesn't seem to be a spot for it in the E&M section of the
DCS. It's not just about producing charge or induced charge. The
instructor referred to it as an example of force at a distance, and there
is the challenge aspect that is meant to make the students think of
non-contact forces. So I thought maybe it could go in the Mechanics
section under contact versus non-contact forces, but there don't appear to
be any demos on this topic. That is surprising in itself, but what I'm
really after is finding a classification for this demo. Any
suggestions? Thanks in advance...



Jerry DiMarco
Manager of Lecture Demonstrations and Instructional Labs
Montana State Univ., Physics Dept.
Bozeman, MT

Our Motto: "There's a demo in there somewhere."
From Wed Apr 27 11:34:35 2005