Perpetual motion machines are machines that produce an unlimited supply of energy, or just never stop. Inventors have tried for centuries to find a working perpetual motion machine, but all have failed, sometimes producing novel ideas, though. It can be shown using the First (conservation of energy) and Second (entropy can never decrease) )Laws of Thermodynamics that any perpetual motion machine is impossible, even though people still try in vain to find them.
Most perpetual motion machines are based on a simple machine, the overbalanced wheel, which was invented during or before the Middle Ages. The idea is that the weighted rods are on hinges so that they stay close to the wheel while going up, and stick out when going down on the wheel, so that the right side will always have more weight, and the left side will always have less, and so the wheel, once started, should never stop.
The problem with this idea is that there are more rods on the left side, and so the weights balance out, and friction eventually brings the wheel to a stop. Many other types of overbalanced wheel have been tried, such as rolling balls inside a wheel, rolling balls on tracks outside a wheel, adding more hinges, and adding complex linkages which don’t really do anything.
Many attempts also have been made with buoyancy as a factor, such as a chain of ping-pong balls entering a cylinder of water on the right side of the chain, which would supposedly provide more than enough lift for the next ball to enter the chamber, and so on. The problem of having no water spill out of the chamber when the balls enter it is, of course, another problem!
Some perpetual motion machines are so crazy that they appear to be jokes. For example, there’s Zimara’s windmill, a machine that goes roughly as follows: The windmill is turned, which squeezes the bellows, which makes air travel through the pipe ,powering the windmill, which squeezes the bellows… and so on.
Of course, on each run, some air particles will miss the windmill, resulting in energy escaping from the system, which eventually stops.
Another great example of a “joke” perpetual motion machine is F.G. Woodward’s wheel. The wheel, supposedly unbalanced on the top roller, will try to rotate counter-clockwise and go down, except that it will not go down because of the bottom wheel, so it will rotate forever.
Any checking with a physics engine, doing force and torque analysis, or just rotating the entire thing will show that it will eventually stop due to friction, like all of the other machines.
Despite the number of proofs of impossibility and failed attempts, a quick look at the internet easily shows that people are still trying to find the right configuration of springs and gears for an impossibility.