Perpetual Motion
by
Robert Nemiroff
Michigan Technological University
Physics X: About This Course
• Officially "Extraordinary Concepts in Physics"
• Being taught for credit at Michigan Tech
o Light on math, heavy on concepts
o Anyone anywhere is welcome
• No textbook required
o Wikipedia, web links, and lectures only
o Find all the lectures with Google at:
 "Starship Asterisk" then "Physics X"
o
http://bb.nightskylive.net/asterisk/viewforum.php?f=39
Perpetual Motion
is ...
• technically, something that is always in motion.
• practically, a machine that generates energy from nothing.
However,
• Newton's law indicates that anything that starts in motion, remains in
motion, so in this sense perpetual motion is expected.
• Machines that generate energy from nothing have never been found
and are now considered a waste of time.
Perpetual Motion Machine:
First Kind
Perpetual motion machines of the first kind generate energy from
nothing.
This violates the local conservation of energy, and since this energy
can be used to generate heat or work, it also violates the first law of
thermodynamics:
1st Law: "The change in the internal energy of a system is equal to the
amount of energy added by heating the system minus the amount lost
as a result of the work done by the system on its surroundings."
Perpetual Motion Machine:
Second Kind
This type of perpetual motion machine uses heat as a power source
directly and continuously, without the flow of heat to a sink. This violates
the second law of thermodynamics.
2nd Law: "Heat (macroscopically) cannot flow spontaneously from a
material at lower temperature to a material at higher temperature."
Perpetual Motion Machine:
Third Kind
This type of perpetual motion machine relies on eliminating
friction. Technically, this is not so much an energy generating machine
so much as an energy storage device.
It is not possible to move with zero friction, so although low friction
devices are real, zero friction devices are not.
Perpetual Motion Machine:
Useful Thought Experiments
At least two classic though experiments seem to create perpetual
motion machines.
•
•
Maxwell's Demon (analyzed in another lecture)
Brownian Rachet Wheel
Perpetual Motion:
Brownian Ratchet Wheel
Perpetual Motion:
Brownian Ratchet Wheel
A ratchet wheel with cogs has a paw that allows it only to rotate in one
direction. Random brownian motion of the air molecules strike the
wheel, sometimes causing enough motion so that it clicks forward one
cog. The paw prevents it from even clicking back. Is the slow rotation
of the wheel perpetual motion?
1. Yes, you've done it!
2. No.
3. It depends in how many dimensions the paw can move.
Perpetual Motion:
Brownian Ratchet Wheel
No. The wheel will only rotate as expected when the the ratchet and
paw are significantly colder than the surrounding air or the heat
bath. Then the device works by tapping into the heat flowing from the
heat bath to the wheel.
When everything is the same temperature, the paw may have its own
Brownian motion and will allow the wheel to go in either direction.
Perpetual Motion:
Magnetic Tower
Balls are pulled up a ramp by a powerful permanent magnet but then
drop through a hole at the top, returning them to their original position.
Perpetual Motion: Magnetic Tower
Why doesn't this work?
1. Any magnet powerful enough to pull the balls up the ramp would be powerful
enough to keep them from dropping through the hole.
2. The rolling ball would at first be attracted to the magnet, but after it rolled its
polarity would reverse and it would then be repelled from the magnet.
3. The system works, but there is no way to extract power.
4. The electric companies kill anyone who gets too close to making this work to
protect the profit of their investors.
Perpetual Motion: Magnetic Tower
Why it doesn't work:
1. Any magnet powerful enough to pull the balls up the ramp would be
powerful enough to keep them from dropping through the hole.
Perpetual Motion: Float Belt
Hollow balls float up through water, only to be pulled back down as they
descend in air.
Perpetual Motion: Float Belt
Why doesn't this work?
1. There is no way to push the balls in at the bottom without losing
water.
2. Pushing the balls in at the bottom will take at least as much energy
as gained from the balls floating up and the falling down.
3. This will work only so long as the water is cooler than the ping pong
balls.
4. A team at Brookhaven is now nearing break-even energy for device
that works on the same principle.
Perpetual Motion: Float Belt
Why it doesn't work:
2. Pushing the balls in at the bottom will take at least as much energy
as gained from the balls floating up and the falling down.
Perpetual Motion:
Conservative Forces
A conservative force creates work on a particle that is independent of
the path taken. Therefore, paths that return to their starting point can
gain no work -- no energy. Therefore, a conservative force field cannot
be used to create a perpetual motion machine that generates energy.
Examples of conservative force field include Newtonian gravitational
force and Coulomb electric force.
Perpetual Motion Machines:
The US Patent Office
Many people try to patent their own perpetual motion machines. The
US Patent office will no longer grant patents to machines that it feels
are perpetual motion power generators, without a working model.
Some people try to create machines so complex that no one could
determine their efficiency without such a model.
Perpetual Motion Machines:
Complex Hoaxes
Examples: Machines that are powered by a cleverly hidden
person.
http://www.museumofhoaxes.com/hoax/Hoaxipedia/Perpetual_
Motion_Machine_of_Charles_Redheffer/
Perpetual Motion Machines:
RJN Advice
If you have created a true perpetual motion machine from which you
create free energy, please do not hold press conferences and tell
everyone. Please start creating power from your machine and selling
it. The electric company MUST buy it, and you can make a fortune.