Friday, February 18, 2011

The Real Perpetual Motion Machine

Thermodynamics states that it is impossible for us to create a perpetual motion machine, that is a machine that can run forever on its own power without putting any work into it. And it's true, we can't. If you have an engine, you know that you have to fuel it in order for it to run. The compression of gasoline in our cars causes an explosion and the explosion pushing the piston up and down and then it happens again. Eventually the fuel runs out and we have to add more energy.

One thing that has always disturbed me thermodynamically speaking is heating and cooling. When you do something it almost always produces heat as a byproduct. If you want to cool something that too produces heat and is very energy inefficient unless you can power your air conditioner with an endothermic reaction (you can't but that would be cool, literally ahahahaha!). It always puzzled me why heating wasn't free both economically and thermodynamically since it is always significantly easier to heat than to cool. But I digress...

Anyways it dawned on me that nature found a loophole in it's own rules. Think of the Earth and the Solar System. Ladies and gentlemen, I present to you the first and only perpetual motion machine energy source, gravity!

Now I will agree that I'm probably a bit on the exaggeration side, because honestly how could nature break it's own rules? We didn't create these rules, we've just learned them along the way. But let's think about this for a second. When we speak of renewable energy what do people mean? Generally they are talking about solar power, wind energy, hydroelectric dams, etc.

Well solar is not really renewable. Sure the sun is burning bright now but in about 30 billion years (maybe way longer) the white dwarf that our sun will become will cool to the point that no light will be emitted from it and we will just sit here freezing our tails off. Unfortunately the earth will long be gone by then so I guess we don't need to worry. And 30 billion years is a long time so it is essentially renewable (unless we start harvesting the sun for power), but my point is the sun runs on energy and that will in time die out.

Waterfalls, and wind are generated from the same source however. Water falls because of gravity. Wind is formed because our atmosphere is a fluid and since the Earth is spinning (because of gravity) the fluids in the atmosphere are sloshing around making havoc and rain and wind.

So it seems that gravity is the most renewable source. Gravity creates a force and if an object is moved a distance do to that force then work is generated. So water falling is technically the Earth doing work on a water source. But let's think about what gravity is before me make any rash decisions that could save all of humanity.

Gravity is a weird side effect of mass. Each atom has it's own gravity but because atoms are so small and gravity is so weak they don't really interact with each other that way. But stick several googles of them together and things start happening. The mass of all those atoms start adding together and generate a gravitational attraction to other massive objects. I'm not too sure about this, but in my head I picture little atoms with little ray guns that shoot out gravitons (the particle that supposedly carries the gravitational force). One won't do much, but lots of them together add up and make stuff happen.

But there is something else to think about. Where does the energy from this come from? After all, everything has to have an energy source. Even light just doesn't appear out of nowhere. Well we all know that E=mc^2, thanks to Albert Einstein, and while that equation was used for nuclear physics it does have some merit here. It basically says that energy and mass are related. In fact mass is just another form of energy, like heat (which thinking about it like that just freaked me out). When something cools it does lose energy, but that means the energy just goes somewhere else. Now, I don't know the intricacies of gravity, but I'm pretty sure that the Earth isn't getting smaller every time something falls.

After all, the Earth is pulling on everything around it. In fact we are all pulling on everything around us, no matter how small or big it is. So where does that energy go? And to that I can honestly say, I have no idea! Maybe the Earth is getting smaller, but maybe because gravity is so utterly weak (compared to all the other universal forces) that the conversion of mass to something else is almost nonexistent. Phew, I thought I would have to delete this whole post for a second.

Well now that I hand waved over that analysis, let's get back to the topic at hand. Waterfalls are sort of a perpetual motion machine. The only reason they aren't is that one day all the water on the top will fall to the bottom. That's just how it works. Luckily the Sun heats up the water, causes it to evaporate and then it rains on the top reservoir again refilling it. But what if that never happened? Then what? Well look at the Earth. It goes around the sun every year, has been doing it for the past 4 billion years, and will continue to do it until the sun gets so large that the earth will just be turned to molten junk, but it in principle will still revolve.

We can even use this same principle to our advantage and we do to keep objects in orbit around the Earth (satellites, space stations, garbage). We can also use gravity to propel a mythical object called a gravity train. I've actually worked out the equations for this in my undergrad. Suppose you could have a tunnel that goes through the Earth. Now you drop an object down into that tunnel. The object will oscillate back and forth for all eternity. You could create an elevator that uses the Earth's gravitational pull to power it. We could also put a turbine in the tunnel and drop some water down it so it will oscillate back and forth turning the turbine forever.

But of course, that will never work. The friction generated from turning the turbine and the water sliding down the tunnel and from air resistance will eventually make it so the water will come to a stop. So for now we will have to let nature break it's own rules and we'll just have to play by them.

No comments:

Related Posts with Thumbnails