From early PSSC days, the "constant speed vehicle" has been portrayed as a
track-laying bulldozer of some sort. If the expected congruences apply, it
is a constant velocity vehicle as well. Relative motion in two dimensions
is often undertaken by having one dozer pull a large flat sheet on which a
second dozer is moving to be examined in the room's frame of reference.
But if the second dozer is started from off the large sheet, on the carpet
let's say, and made to intercept the moving sheet, an interesting
refraction occurs at the interface. The reason is simple. One track is
getting traction on the moving sheet before the other. Depending on the
angle of incidence, refraction can be observed either towards the normal or
away from it. This behavior can be predicted by noticing which track would
enter the moving sheet first or leave it last since this is what produces
the couple that turns the vehicle.
If the towed sheet has parallel edges, it is observed that the refracted
dozer makes parallel paths on the carpet before and after being transported
by the sheet. One presumes the shape of a prism or lens section could be
towed.
The question for the list is:
What physical systems could be usefully modeled with such an arrangement?
It is typical, but not necessary for both dozers to have the same speed.
The dozer blade might be regarded as an element of a wavefront or the path
of the dozer, a ray, e.g.
Tom Ford
The Science Source
Manufacturer of Science Educational
and Design Technology Equipment
P. O. Box 727
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e-mail: tomford@thesciencesource.com http://www.thesciencesource.com