Why is this not a “perpetual-motion machine?”
Before I begin, let me state clearly that I fully accept the laws of therodynamics. I do not for one second believe I have stumbled onto something astounding here. Rather, I assume I have either overlooked something important, or am misunderstanding the question. I need help in seeing where I’m going wrong.
(I would also respectfully request that those who do not accept Newton’s Laws please do not hijack this thread. Rather, please post your comments in Great Debates or The Pit or some other forum where the scientific method is not a prerequisite.)
Now, then…
I have always understood a “perpetual motion machine” to be a system that puts out more energy than it takes in as fuel. If this is a flawed definition, let me know. If not, read on…
Imagine a bathtub, pushed up against a wall. About two feet above the rim of the tub, affix two rods to the wall, jutting straight out across the tub. They should be about a foot or so apart. If you want to build a framework on the near side of the tub to hold those rods steady, be my guest.
Drape a bath towel over the two rods. The edge of the towel draped over the left rod should hang down about six inches; the edge draped over the right rod should fall into the tub. So basically what you have is an upside-down “J.”
Put a plug in the drain and fill the tub with water. Capillary action will draw water up into the towel, over the rods, and come dripping off of the short end. There is no “fuel” involved - the whole thing is powered by gravity and capillary action.
You could even put a small water wheel under the dripping end, attach magnets and wires, and generate an electric current. Granted, the output would probably be very small, but it’s still energy coming out with none going in.
So, where am I going wrong here?
One could argue that the water is a “fuel” of sorts, and it will eventually evaporate. But all you need do is seal off the bathroom, making a closed system.
Friction will eventually wear out all the pieces. Water moving through the towel will slowly erode it. The tub will eventually rust. But those are failings of the material, and not of the system. Do they really count?
Similarly, the Sun will eventually go supernova, calling a halt to the experiment. Long before that, earthquakes will topple the building. But again, those are external forces - do they really count as a system failure?
Of course, just because there is no “fuel” doesn’t mean there was no energy going into the system. It took energy to make the tub, the towel, the rods, even to mine the metal and pump the water. Do those energy costs need to be factored in? It seems to me the electricity you get out of the system might never make up for the production.
So, there’s my daydream. Punch it to pieces. Thanks.
– Beruang