they apply physics incorrectly; and ( 2) experimental
— if you build and test them, they don’t work.
Simon Stevin’s Ball-Ramp and
Woodward’s Wheel
Flemish mathematician and engineer Simon Stevin
(or Stevinus, 1548-1629) analyzed a device consisting of a chain of balls on a frictionless double ramp.
The chain was supposed to slide counterclockwise
since there was more weight of chain to the left of
the vertex. But Stevin’s analysis showed that the
system had no inclination to move at all, because
it was always in static balance. These results led
Stevin to formulate a fundamental principle of
mechanics, known as Stevin’s Principle of Virtual
Work, which is found in textbooks even today.
Something about the notion of perpetual motion
tantalizes those with restless minds, who think,
“Perhaps there’s some principle of physics, as yet
unknown, that we might discover if we just alter
the design a bit.” So, through the centuries, these
people tinkered with the designs, in a fantastic variety of ways, until the proposed machines became
hopelessly complex. Such is the perversity of nature
that none of them worked.
Some inventors were so confident of success that
they included a brake in their designs to prevent
the machine from turning so rapidly that it would
tear itself apart. They needn’t have worried.
Some drawings included an arrow showing which
direction the inventor supposed that the wheel
would turn. This is especially helpful; without it,
we physicists wouldn’t have the slightest idea which
way the wheel should turn. If laws of physics allow
the wheel to turn equally well in either direction, you
can be quite sure the wheel won’t initiate motion
by itself and won’t sustain motion forever when
you give it a push.
By the 19th century, there was a refreshing return
to simple basics. F. G. Woodward proposed a hoop
wheel supported by two rollers. This is about as
simple a design as you can imagine. Since the
wheel always has more weight to the left of the
rollers, that side should move down, as the arrow
indicates. But the wheel stubbornly defies that
“logic,” refusing to budge.
PERPETUAL OPTIMISM
Inventors before the 17th century had no physical laws of energy and momentum that would
72 Make: Volume 09
Simon Stevin’s ball-ramp
Model of Stevin’s chain
Richard’s overbalanced chain
