| Why not use a sound trigger? The response
of a sound trigger would lag that of a photogate. The difference might be
only a millisecond, but that could be all the time it took for the towel to
make its flip. The event would be over before the first flash discharged.
(In fact, this is what the students found in some initial testing.)
The odds against performing a successful experiment
were high for the following reasons:
- The tip of the towel had to be targeted for a very
small region defined by the intersection of the narrow light beam and
the field of view of the camera.
- The towel had to reach its greatest extent just
after it reached the target region. (In experimentation, it was found
that the time window was less than a millisecond.)
- The towel had to be snapped with sufficient force
and with the right technique to produce the cracking sound that would
signal, if the hypothesis were correct, that the towel tip had exceeded
Mach 1.
- The towel had to be snapped in near total darkness,
since the camera would be running continuously.
A video camera recorded images directly to a
freeze-frame VCR. This method of recording was chosen for two reasons:
- The ratio of failed to successful snaps was
expected to be quite high for the reasons listed above. Videotape would
be an inexpensive medium for recording.
- With a freeze-frame VCR, images could be played
back immediately. Estimates of the speed of the tip could be made
from the TV display.
As far as the students knew, no one had attempted such
an experiment before with a towel. Spence volunteered to be the towel
snapper. As you will see in the pages that follow, he deserves the
title of "world's most accomplished towel snapper".
Go to Initial
Experimental Results |
