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|“The Three Laws!!” • May 17, 2006|
Thermodynamics — Entrance Stage Left!!
Roger and I were cruising over to Burt’s Burger Barn the other day and I happened to notice a bumper sticker on the car ahead of us at a red light. It said, “Maybe the Hokey Pokey IS what it’s all about!”
WELL — I have a hard time believing that a silly song and children’s dance is the TRUE secret of the universe, (although you can’t really be too sure when you’re talking about DNA’s!!)
However, the bumper sticker did kick start the blond brain cells into thinking about what the universe REALLY is all about! SO — put on your thinking hats and little Meredith is gonna school you in the Three Laws of Thermodynamics! (And yes, the capitals are both intentional and justified!!)
The following quip seems to accredited to a number of different people so I don’t know exactly who said it first, but the three laws can be summed up as:
1. You can’t get something for nothing!
2. You can’t even break even!
3. You can’t get out of the game!
As crummy as that sounds, it’s even worse because not only is it absolutely true, there are NO exceptions. Those three laws are the absolutely most fundamental rules in understanding how EVERYTHING works! And I do mean everything! Whether you are trying to understand the sun, or how grass grows, or how galaxies form, or how your car works, or even how YOU and I work, you always end up back at those three laws!
If something “violates” those three laws, then that something is impossible!! Absolutely!! Our universe can not EXIST without them!
Now having said that, there is someone furiously typing an e-mail at this very second that says, “Oh Yeah? Then what about the Big Bang, Blondie?”
To nip that in the bud, the Big Bang that created our universe of “something” from “nothing” does seem to violate the three laws — BUT — (and a very BIG BUT indeed) — the three laws apply TO OUR UNIVERSE — not to whatever system that existed before and created our universe! Translation, there may have been different rules that applied before the Big Bang, but at the instant that it happened, (by whatever process and laws,) the three laws have been in force ever since! Everything since “time zero” in our universe has “obeyed” the three laws and it always will. If you have “proof” that they have been violated, then your “proof” is wrong.
OK — so they are important — but what the dickens do they really mean?
Let’s start with the first one. This was originally two concepts (laws) called the Conservation of Energy and the Conservation of Mass. After Einstein came along and showed that mass is just a VERY concentrated form of energy, (that’s where the E=MC² thing comes in — that is that energy is equal to mass multiplied by the speed of light squared,) we refer to the Conservation of Mass-Energy and cover both former laws.
So what does that really mean? Actually it is nothing but common sense! If you go to the store and buy five pounds of potatoes, all you have got is FIVE POUNDS OF POTATOES. You can’t “magically” turn it into TEN POUNDS of potatoes. You can’t end up with more than you started with!
Similarly, if you stick a fresh pair of AA batteries into your Walkman, all you are going to get is the power contained in those batteries. Eventually they are going to run down, that is, all the energy stored in them is going to be used up, and your Walkman is gonna stop. Just as you can’t end up with more potatoes than you started with, you can’t end up with more energy than you started with.
Or in scientific terms, the mass and energy are “conserved.” Conserved means that whatever you start with is what you end up with — no more — no less. The mass and energy may be changed in form — potatoes can become mashed potatoes and eventually part of someone’s thighs, but the same mass is always there! The chemical energy in the battery gets changed to electrical energy to run the Walkman which turns the electrical energy into “sound energy.”
People have been trying for a long, long time to come up with “perpetual motion” machines that violate this law — and every one of them doesn’t work and can’t work! While a lot of “interesting” schemes have been proposed, they all end up in principle as something like this: Mechanically connect an electric motor up to an electrical generator then take the power output from the generator and connect it to the motor to power it — and then take the “excess” electrical power and do something useful with it — like run Meredith’s servers!!
We’ll see that this REALLY runs afoul of the Second Law in just a moment, but for the time being, it violates the First Law because you end up with more energy than you started with. In the absolute best case, if you had a “perfect” motor and a “perfect” generator, then the motor could power the generator and the generator could power the motor. But even with “perfect” components, there could NEVER be any excess energy. It would take ALL the generator’s output to run the motor and all the motor’s output to run the generator.
SO — to make it short and sweet — “You can’t get something for nothing!”
At this point, hopefully everyone is nodding along and saying, “Makes sense!”
Well — that’s a step in the right direction — but it REALLY starts to make sense when you apply it to EVERYTHING! Remember, there is no way to cheat! You can’t avoid the three laws of thermodynamics anymore than you can avoid gravity! AND — I want everyone to remember that because in a upcoming M Column I’m gonna tackle the most sacred of all cows — DIETING! It is remotely possible, but highly unlikely, that at sometime someone has proposed a fad diet that DOESN’T violate the laws of thermodynamics — but I’ve never seen it!! That’s why they don’t work — and can’t work — and are totally impossible — and violate the most fundamental laws of the universe! But — save the irate e-mails until you’ve read that column. It’ll be along as soon as I can get my courage worked up!!
OK — moving right along, let’s take a look at the second law — “You can’t even break even.” Sounds like a pretty crummy game, right? It is!!
Let’s go take another look at our motor-generator perpetual motion machine thingie. Suppose the motor produces “X” amount of mechanical energy in the form of a rotating shaft connected to the generator. The generator converts this “X” amount of mechanical energy into “X” amount of electrical energy which flows through the wires back to the motor which takes “X” electrical energy and transforms it into “X” mechanical energy. The energy circulates back and forth between the motor and generator and similarly changes from mechanical to electrical to mechanical. So far, so good. There is no left over energy as that would violate the first law, but at least the thing keeps chugging on forever.
EXCEPT — and it’s a BIG EXCEPT — we are assuming that the motor gets “X” electrical energy and “perfectly” turns it into “X” mechanical energy and that the generator “perfectly” turns “X” mechanical into “X” electrical energy. Before we get to the third law and find out exactly why there is NO CHANCE of doing this perfectly, we can from common experience already see the problem. Pick the electric motor of your choice — an electric mixer, drill, etc. and turn it on. Now put your hand on the case — kinda warm, right? That heat you are feeling is the energy loss because the motor is not perfect. In other words, the electric motor, mixer, drill, whatever get “X” electrical energy and turns it into “Y” mechanical energy and “Z” heat energy. The “Z” heat is a total loss and can’t do anything useful. And the generator does the same things. It also gets hot and energy is lost. So — a little energy is lost in each loop and after a couple of loops between the motor and generator all of the energy has been lost as heat and the “perpetual motion machine” has become a “perpetual stationary machine.”
You can do a better job of engineering the motor and generator to minimize the energy losses, but you can’t ever make them perfect. Or as the second law says, “You can’t even break even!”
Now — to see why we are going to be frustrated at trying to make a perfect machine, we take a look at the third law — “You can’t get out of the game!” — which is another way of saying — “you can’t make perfect machines — there will ALWAYS be losses.”
If you use the best bearings possible in the motor and generator to minimize friction there will still be losses. Friction is part of the problem but not all of it. The real fundamental problem is found in the third law in which we find that anytime you convert one form of energy to another form there will always be losses!! And those losses are unavoidable.
To understand this, let’s go back to when the three laws were just getting worked out. It was the start of the industrial revolution and everyone was trying to improve the newfangled steam engines. After a lot experimentation, the science of thermodynamics was created. If you look at the word, “thermo” is a fancy word for heat and “dynamics” is an equally fancy word for movement. So thermodynamics is about “heat movement.” Or it was when it was first developed because there were very few other forms of energy. Even though it really applies to all forms of “energy movement” and not just heat, the name has stuck around. No one is more conservative in terminology that scientist and engineers.
OK — so it’s about energy movement — so what? Well — energy always “runs down hill.” That is, it always runs from a high concentration of energy to a low concentration of energy. For example, when something is hot it has a lot of energy — something that is cold has less energy. Energy “runs down hill” so energy flows from the hot thing to the cold thing. That’s why hot things cool off — they transfer their heat to the air, water, whatever around them that is cooler and therefore less energy dense. Of course when the cold thing gets some heat energy it warms up, but eventually the two reach equilibrium and both has the same energy density and thus the same temperature.
SO — suppose you’ve got a really hot thing that has got a lot of energy in it — and you want to get the very last dregs of energy out of it and transferred somewhere else. To transfer it, the thing you’re transferring to must have less energy than the hot thing — that is, it has to be cooler. And the cooler it is, the more energy it can absorb from the hot thing before they both reach equilibrium — that is the same temperature.
So we start off cooling the hot thing down and extracting energy — and keep cooling — and keep cooling — and keep cooling. And while the hot thing is getting cooler and giving up energy, it still hasn’t given up ALL it’s energy which would be required for PERFECTION. So we keep cooling until we get down to 459 degrees Fahrenheit or 273 degrees Celsius below zero and our cooling stops! This temperature is called absolute zero and it really is ABSOLUTE! You can’t get anything any colder than that! And guess what, even if you cool the hot thing all the way down to absolute zero — it STILL has some internal energy that it just won’t let go of! No further cooling is possible and no further energy extraction is possible, but even though you have gone to a GREAT deal of trouble to get it that cold, you still are leaving some energy behind in it — and that energy is lost and gone forever because you can’t get it out!!
So — there is always some energy left behind and that energy is lost.
Absolute zero bothers a lot of folks and they ask, “Well — why can’t you make it colder?” The reason is that absolute zero is not just a temperature but is actually derived from the third law — that is absolute zero is the temperature at which you can’t get anymore energy, (heat,) out. The heat isn’t zero, but it is at a minimum.
Let’s try one more example or actually an analogy that may make this a little clearer. Suppose you were going to make a waterwheel and you want it to be as efficient as possible. That is, you want to extract as much energy from the falling water as possible and transfer it to your wheel.
If the water level is below the wheel then obviously no water is gonna fall on the wheel and turn it. If the water is at the same level as the wheel, again nothing it gonna happen. The only way for it to work is for the water to be ABOVE the wheel and fall on it — in which case the wheel will extract the energy of the falling water and turn it into useful mechanical energy for grinding wheat or something. And the higher the water is above the wheel, the more energy it’s gonna have and the more it’s gonna transfer to the wheel.
So to get more energy, we need to keep moving the water higher and higher. Ten feet produces more energy than five fee. A hundred feet produces more still — and so does a thousand — and a mile — and a thousand miles — and a billion miles — and a light year — and a billion light years. But even then, we could get more energy out of the water by moving it still higher. In fact, the only way we could get ALL the energy is if the water was an INFINITE distance above the wheel. And infinite distances, just like perfect machines are impossible!!
SO — no matter how hard you try, the third law is sitting there like the Cheshire Cat grinning away saying “You can’t get out of the game” and therefore can’t beat the first two laws.
AND — before some smarty pants sends me an e-mail about water falling into a black hole — I’ll just say — stay tuned for a later M Column and go read up on Hawking radiation!!!
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Last Updated: May 2006
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