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."

Comments

The problem with your idea is thermodynamics

[MyNameIsFred]

The problem with your idea is thermodynamics. Thermodynamic analysis will tell you the maximum efficiency that an engine can acheive. Look up the Carnot engine (or cycle) for a good discussion. A Carnot engine is the most efficient engine possible, nonetheless, the thermodynamic limits are a killer. Throw in friction, realistic melting points for materials, etc. and the world is a dreary place. Engines will NEVER approach 98% efficiency.

Re:Perpetual Motion Machines of the First Kind

[Dynedain]

Its exactly like connecting an internal combustion engine up to a nearly infinite tank of gasoline. Its not a perpetual motion machine, it simply has a fuel source that is seemingly infinite (in this case, heat).

Yes, no, and maybe.

[freeweed]

You're sort of mixing up what you're talking about, but mostly, you're on track. It's trivially easy to cause something to obtain perpetual motion - as many other posts have pointed out, just toss something into space. Odds are it'll keep going forever. Perpetual motion isn't hard at all (after all, Newton's laws effectively demand that it be possible). A perpetual motion MACHINE, on the other hand...

As for weather, the problem is you're relying on an external power source - the sun. Turn that off, and boom, no weather (well, eventually anyway). You are correct though, we can use this energy that's just sitting around and gain more than we put into something. In fact, this is how our entire planet survives - both its organisms and our modern society. Think hydroelectric damns and wind turbines - they're just using something that's there anyway. And plants take advantage of the ever-present sun to store chemical energy within themselves, which other organisms then use when they eat said plants, etc.

The problem still lies in self-contained systems. A friend of mine took years to believe me that you couldn't run a ship (assuming no wind outside) with windmills powering a motor that actually powers the ship. Friction is a bitch :)

Re:People will always try

[dhovis]

Actually the Carnot cycle puts a limit on the conversion of heat energy into any other form of energy (kinetic, potential, electrical, magnetic, chemical, nuclear, etc). However, heat is the only form of energy so limited. Other conversions, say chemical => electrical are only limited by the second law of thermodynamics. For that matter, converting any other energy to heat can be very efficient. Electrical energy => heat, for example.

So, something like a microturbine is limited to ~30% efficiency for electricity generation. Larger plants can get up to 35% efficiency. A fuel cell has no such limit and could potentially reach into the 90% range for efficiency of electricity generation. Hybrid fuel cell-turbine generation systems are being tested which have efficiencies of over 50% and they speculate that they could hit 70% or more. The problem with such a system is that the upfront cost is very high and it does not get offset by the savings in fuel. Not yet, anyway.

Remember too that conversion of any energy to heat can be very efficient. Natural gas furnaces can be extremely efficient, as high as 97%. That's because converting chemical energy => heat is not a Carnot limited process, and is only limited by the second law of thermodynamics.