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[Physltest] [Phys-L] A Reactionless Force Fallacy



An instructor here sketched a machine which he suggested would move without
reaction on the floor surface on which it moved. One can readily extend
his concept to the possibility of a rotating device levitating from the ground,
simply on the strength of the electrical power from an umbilical.

This underlines the physical fallacy underlying his device, but I would
like
to succinctly explain the fallacy, without falling back on the usual
momentum
conservation rules.

The machine may be described briefly in this way:
A wheel is free to rotate, and on its spindle is fixed a second wheel, canted
at an angle to the first but constrained to turn at the same angular rate
as the first wheel by an electric motor drive, so that the distance of
two adjacent spots on the two "tire" surfaces cyclically varies from a
minimum to a maximum in the course of each joint rotation.
Numerous wire cables are fixed on the periphery of one,
and fed through pulleys on the adjacent surface of the other wheel
in order to whirl weights using tethers which effectively shrink
and stretch during each revolution.
These weights evidently describe a circle(?) whose center is displaced
from the pivot points of both wheels.
As the peripheries of both wheels move jointly at a constant speed,
the radial wire tethers evidently accelerate to where the wires are
longest, and decelerate as the tethers shorten.
He argues that there is a force due to these wires on their fixings,
which act in one predominant direction in the room's frame, to
provide thrust.

How would you explain the misapprehension?


Brian Whatcott Altus OK Eureka!
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