It appears Vern Lindberg saw the show and remembers it in a way that
explains the answer given.
My point in this message is to respond to Jim Green's statement: "As I
recall from the brief glimpse I had the question had to do with the standard
two pulley problem..."
I don't think there is a "standard" two-pulley problem. There are at least
two significantly different options. In option-A (the one Jim thought he
saw) neither end of the cable attaches to the lower pulley... it always runs
through it some number of times, so the number of cables supporting the
lower pulley is always an even number. In option-B (what Vern thought he
saw) one end of the cable attaches to the lower pulley and later returns to
go through the pulley some number of times. For option-B the number of
cables supporting the bottom pulley is always an odd number.
I find option-B (odd number of cables going to the lower pulley) is the one
that most often gives people problems. I have seen several textbooks used
in middle-school science that draw pictures of this, but fail to count the
odd cable (the one attached to the bottom pulley) as a supporting cable.
Some books even define the mechanical advantage as "twice the number of
times the cable passes through the lower pulley." Of course that "rule" is
only correct if the cable does not attach to the lower pulley, and from what
I have seen "in the field" it is just as likely to attach to the lower one
as to the upper one. For some reason, few middle-school textbooks give the
simple rule of just counting the number of cables that run to the lower
pulley.
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