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The Museum of Unworkable Devices
Jippy_ writes "The quest for perpetual motion has been going on since at least the 11th century according to this site, and scientists have been getting it wrong ever since. Take a gander at some of the most valiant efforts (and ultimately the biggest failures) in trying to beat the laws of physics through the last 1000 years, along with other impossible inventions and devices."
When I was younger, in early high school, I discovered that my father was trying to build a perpetual motion machine in his basement workshop. It was a rotating wheel with slots that contained ball bearings. The idea was that the bearings would roll in the slots in such a way that the wheel would constantly be unbalanced, causing it to rotate forever. He hadn't quite gotten it to work, of course, and was concerned about the angle of the slots and friction at the hub. I had taken some physics by then, and tried to explain to my dad about conservation of energy and how his machine, in principle, could never work. Maybe he was already discouraged by then, but he quit working on it shortly after that.
Make a difference: move to a swing state.
I got the page to load before it got slashdotted, and it looks like these are all perpetual motion machines of the first kind. These machines violate conservation of energy.
Perpetual motion machines of the second kind don't violate conservation of energy, but they rely on a decrease in entropy. With a machine like that a ship could run an engine that extracts energy from the ambient water temperature to do work, leaving a trail of colder seawater behind the ship. That doesn't violate conservation of energy, but it does cause a global reduction of entropy.
It takes more cleverness to come up with a machine of the second kind, and it's usually less obvious why they don't work.
Here's a machine like that. Assume we have a propellor made of some heat resistant material like ceramic, inside a larger ceramic housing in which it is free to rotate. Stick a big permanent magnet around it so that there is a magnetic field running through it, parallel to the propellor axis. Now inject a hot plasma of some sort into the device. Electrons in the plasma move in tight little counterclockwise circles because of the field. Protons move in much wider clockwise circles (they're heavier), so they hit the propellor blades preferentially in one direction and make it rotate.
Of course the plasma is going to cool down quickly if the protons in it are imparting kinetic energy to the propellor. So as a perpetual motion machine of the first kind, it's obviously going to run down and stop. But take the whole machine and drop it on a planet where the ambient temperature is high enough to keep the plasma hot. As the propellor extracts energy, more heat flows into the machine. What's wrong with it now?