To the Editor:
In the Fall 1998 Forum on Education Newsletter, Kenneth Heller views teaching
as transforming students from their initial states to desirable final states,
with some of the latter "forbidden" e.g. by energy conservation. However, "forbidden" perpetual-motion
machines (PMMs) can be pedagogically helpful for understanding the "allowed" laws
of physics. So can hypothetical physically-valid schemes which resemble
PMMs. Their study, which may also involve many other useful concepts and
techniques, could become interesting introductory-course team projects
integrating science and engineering, as recently called for by many engineering
deans and the National Accreditation Board for Engineering and Technology
(ABET); see, e.g. the Forum on Education 1998 Summer and Spring issues.
In one example, which was actually denounced as a PMM by a Mechanical-
Engineering Professor with a Ph.D. in Physics, packets of lunar material
would first be "slung" electromagnetically from the moon towards earth.
Their original launch kinetic energy would then be amplified gravitationally
by a factor of about twenty on reaching the "edge" of the earth's atmosphere.
Here their homed-in controlled horizontal multiple "impacts" with initially-slow
spacecraft and orbiting generators could convert part of their kinetic
energy into usable craft propulsion and electrical energy. Damaging accelerations
can be prevented e.g. by pre-expanding the packets to low density, and
attaching delicate payloads to the craft by long rotating tethers perpendicular
to the impulse at impact. A fraction of the electrical energy could then
be sent back to the moon by microwave beam, there to launch additional
material and repeat the cycle, seemingly perpetually.
Eventually, of course, the moon would shrink, preserving thereby the laws
of physics. But this would take hundreds of millions of years at present
global energy-consumption rates.
Louis A. P. Balazs
Department of Physics
West Lafayette, IN 47907-1396