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PROFESSOR: Thermodynamics, all right, let's start.

Thermodynamics is the science of the flow of heat.

So, thermo is heat, and dynamics is

the motion of heat.

Thermodynamics was developed largely beginning in the

1800's, at the time of the Industrial Revolution.

So, taming of steel.

The beginning of generating power by burning fossil fuels.

The beginning of the problems with CO2 and [NOISE OBSCURES]

global warming.

In fact, it's interesting to note that the first

calculation on the impact of CO2 on climate was done in the

late 1800's by Arrhenius.

Beginning of a generation of power moving heat from fossil

fuels to generating energy, locomotives, etcetera.

So, he calculated what would happen to this burning of

fossil fuels, and he decided in his calculation, he

basically got the calculation right, by the way, but he came

out that in 2,000 years from the time that he did the

calculations, humans would be in trouble.

Well, since his calculation, we've had an exponential

growth in the amount of CO2, and if you go through the

calculations of -- people have done these calculations

throughout times since Arrhenius, the time that we're

in trouble, 2,000 years and the calculation, has gone like

this, and so now we're really in trouble.

That's for a different lecture.

So, anyway, thermodynamics dates from the same period as

getting fossil fuels out of the ground.

It's universal.

It turns out everything around us moves energy around in one

way or the other.

If you're a biological system, you're burning calories,

burning ATP.

You're creating heat.

If you're a warm-blooded animal.

You need energy to move your arms around and move around --

mechanical systems, obviously, cars, boats, etcetera.

And even in astrophysics, when you talk about stars, black

holes, etcetera, you're moving energy around.

You're moving heat around when you're changing matter through

thermodynamics.

And the cause of some thermodynamics have even been

applied to economics, systems out of equilibrium, like big

companies like Enron, you know, completely out of

equilibrium, crash and burn.

You can apply non-equilibrium thermodynamics to economics.

It was developed before people knew

about atoms and molecules.

So it's a science that's based on macroscopic

properties of matter.

Since then, since we know about atoms and molecules now,

we can rationalize the concepts of thermodynmamics

using microscopic properties, and if you are going to take

5.62, that's what you'd learn about.

You'd learn about statistical mechanics, and how the

atomistic concepts rationalize thermodynamics.

It doesn't prove it, but it helps to getting more

intuition about the consequences of

thermodynamics.

So it applies to macroscopic systems that are in

equilibrium, and how to go from one equilibrium state to

another equilibrium state, and it's entirely empirical in its

foundation.

People have done experiments through the ages, and they've

accumulated the knowledge from these experiments, and they've

synthesized these experiments into a few basic empirical

rules, empirical laws, which are the laws of

thermodynamics.

And then they've taken these laws and added a structure of

math upon it, to build this edifice, which is a very solid

edifice of thermodynamics as a science

of equilibrium systems.

So these empirical observations then are

summarized into four laws.

So, these laws are, they're really depillars.

They're not proven, but they're not wrong.

They're very unlikely to be wrong.

Let's just go through these laws, OK, very quickly.

There's a zeroth law The zeroth law every one of these

laws basically defines the quantity in thermodynamics and

then defines the concept.

The zeroth law defines temperature.

That's a fairly common-sense idea, but it's important to

define it, and I call that the common-sense law.

So this is the common-sense law.

The first law ends up defining energy, which we're going to

call u, and the concept of energy conservation, energy

can't be lost or gained.

And I'm going to call this the you can break even law; you

can break even law.

You don't lose energy, you can't gain energy.

You break even.

The second law is going to define entropy, and is going

to tell us about the direction of time, something that

conceptually we, clearly, understand, but is going to

put a mathematical foundation on which way does time go.

Clearly, if I take a chalk like this one here, and I

throw it on the ground, and it breaks in little pieces, if I

run the movie backwards, that doesn't make sense, right?

We have a concept of time going forward in

a particular way.

How does entropy play into that concept of time?

And I'm going to call this the you can break even at zero

degrees Kelvin law.

You can only do it at zero degrees Kelvin.

The third law is going to give a numerical value to the

entropy, and the third law is going to be the depressing

one, and it's going to say, you can't get to zero degrees.

These laws are universally valid.

They cannot be circumvented.

Certainly people have tried to do that, and every year

there's a newspaper story, Wall Street Journal, or New

York Times about somebody that has invented the device that

somehow goes around the second law and makes more energy than

it creates, and this is going to be -- well, first of all,

for the investors this is going to make them very, very

rich, and for the rest of us, it's going to be wonderful.

And they go through these arguments, and they find

venture money to fund the company, and they get very

famous people to endorse them, etcetera.

But you guys know, because you have MIT degrees, and you've,

later, and you've taken 5.60, that can't be the case, and

you're not going to get fooled into investing money into

these companies.

But it's amazing, that every year you find somebody coming

up with a way of going around the second law and somehow

convincing people who are very smart that this will work.

So, thermo is also a big tease, as you can see from my

descriptions of these laws here.

It makes you believe, initially, in the feasibility

of perfect efficiency.

The first law is very upbeat.

It talks about the conservation of energy.

Energy is conserved in all of its forms.

You can take heat energy and convert it to work energy and

vice versa, and it doesn't say anything about that you have

to waste heat if you're going to transform heat into work.

It just says it's energy.

It's all the same thing, right?

So, you could break even if you were very clever about it,

and that's pretty neat.

So, in a sense, it says, you know, if you wanted to build a

boat that took energy out of the warmth of the air, to sail

around the world, you can do that.

And then the second law comes in and says well, that's not

quite right.

The second law says, yes, energy is pretty much the same

in all this form, but if you want to convert one form of

energy into another, if you want to convert work, heat

into work, with 100% efficiency, you've got to go

down to zero degrees Kelvin, to absolute zero if you want

to do that.

Otherwise you're going to waste some of that heat

somewhere along the way, some of that energy.

All right, so you can't get perfect efficiency, but at

least if you were able to go to zero degrees Kelvin, then

you'd be all set.

You just got to find a good refrigerator on your boat, and

then you can still go around the world.

And then the third law comes in, and that's the

depressing part here.

It says, well, it's true.

If you could get to zero degrees Kelvin, you'd get

perfect efficiency, but you can't get to zero degrees

Kelvin, you can't.

Even if you have an infinite amount of resources,

you can't get there.

Any questions so far?

So thermodynamics, based on these four laws now, requires

an edifice, and it's a very mature science, and it

requires that we define things carefully.

So we're going to spend a little bit of time making sure

we define our concepts and our words, and what you'll find

that when you do problem sets, especially at the beginning,

understanding the words and the conditions of the problem

sets is most of the way into solving the problem.

So we're going to talk about things like systems.

The system, it's that part of the

universe that we're studying.

These are going to be fairly common-sense definitions, but

they're important, and when you get to a problem set,

really nailing down what the system is, not more, nor less,

in terms of the amount of stuff, that's part of the

system, it's going to be often very crucial.

So you've got the system.

For instance, it could be a person.

I am the system.

I could be a system.

It could be a hot coffee in a thermos.

So the coffee and the milk and whatever else you like in your

coffee would be the system.

It could be a glass of water with ice in it.

That's a fine system.

Volume of air in a part of a room.

Take four liters on this corner of the room.

That's my system.

Then, after you define what your system is, whatever is

left over of the universe is the surroundings.

So, if I'm the system, then everything else is the

surroundings.

You are my surroundings.

Saturn is my surroundings.

As far as you can go in the universe, that's part of the

surroundings.

And then between the system and the

surroundings is the boundary.

And the boundary is a surface that's real, like the outsides

of my skin, or the inner wall of the thermos that has the

coffee in it, or it could be an imaginary boundary.

For instance, I can imagine that there is a boundary that

surrounds the four liters of air that's sitting in the

corner there.

It doesn't have to be a real container to contain it.

It's just an imaginary boundary there.

And where you place that boundary becomes important.

So, for instance, for the thermos with the coffee in it,

if you place the boundary in the inside wall of the glass

or the outside wall of the glass and the inside of the

thermos, that makes a difference; different heat

capacity, etcetera.

So this becomes where defining the system and the boundaries,

and everything becomes important.

You've got to place the boundary at exactly the right

place, otherwise you've got a bit too much in your system or

a bit too little.

More definitions.

The system can be an open system, or it can be a closed

system, or it can be isolated.

The definitions are also important here.

An open system, as the name describes, allows mass and

energy to freely flow through the boundary.

Mass and energy flow through boundary.