http://www.nearingzero.net (nz324.jpg)

April 3Thermodynamics

April 5No Class

April 10Fossil Fuels

April 12Times Beach

Video

April 17Video Discussion

Alternative Energy

April 19Global Warming

April 24Your Oral Reports

April 26Your Oral Reports

Physics 6 ScheduleLab

meets Friday

“Pollution is nothing but resources we're not using.”—R. Buckminster Fuller

It’s Course Management Time!

It’s time for everybody to check the grades spreadsheet!

The following homework is absolutely due this week:Tacoma Bridge (HW 2) Climate Video (HW 3)Dumping Ground (HW 4) Energy Patrol (HW 5)Ozone Video (HW 6) Ozone Web Site (HW 7)Energy Calculation (HW 8)

Hand in these assignments by the 5:00 pm Friday, April 7!

The following homework is absolutely due Wed., April 12:

We All Live Downstream Video (HW 9) el Niño Video (HW 10) Great Experiment Video (HW 11)

Any video you “check out” for late viewing is now due at the beginning of the next class period, or you get a 0 for that homework assignment.

Isn’t it exciting when your prof. gets hardnosed?

“We” have to give all students a fair chance to do the homework.

Your environmental Issues.

Worth 25% of your semester grade (25 points). 10 points for completeness (did you do it all), 10 points for thought processes (did you think, or just blurt out the first thing that came to mind) and 5 points for accuracy.Some of the issues are short and easy, others long with nice calculations. Unfair?

Your talks are scheduled for April 24 & 26, and May 1 & 3.We really need 4 days for the presentations! (I’ll use any “leftover” time to finish lectures on energy.)

Some of you get to get your talks over with.

Others will have to wait until the last day.

On today’s attendance sheet, please “claim” a date for your talk. (This is optional for today, but by the end of next week I want all of you to know the date of your talk, so if you don’t “claim,” I’ll assign.)

Some talks last time I taught Physics 6:El NiñoEmpty Ocean Empty NestIllegal DumpingSoil Degradation and ErosionSoil Erosion: Types of ErosionThe Great Plains and the Prarie DogDolphin-Safe TunaHelping Our Planet: LitterDeforestationStorm Water RunoffTimes Beach, MissouriDoes Your Lawn Look Pretty? (Your Water Doesn’t!)SUV’s and the EnvironmentHow Long Would It Take To Fill Up The Earth?Coral ReefsMountain LionsAcid Deposition (Acid Rain)Dangers of the SunGlobal Fisheries: The Pacific NorthwestLandfills

Great Lakes Alive: The Great Experiment

Your comments on this video?

Who made it?

Canadians!

Interesting juxtaposition of the “scientist guy” and the “environmentalist lady.”

I get irked when they claim an element—was it mercury??—as among the “manmade” chemicals found in the lakes. But that’s really nitpicking. (If you have to resort to such an argument in a debate, you must not have much to support your position.)I “love” the frog with parts per thousands pcb’s in its body. A walking hazardous waste dump. You’d probably go to jail if you tried to mail him to somebody!

Some comments of mine:

The most scientifically-grounded video this semester.

Did you notice how the higher up the food chain, the more your body concentrates toxic materials?

What’s up with the Great Lakes today?

It would take a whole course to answer that question!

The video mentioned Areas of Concern.

Remedial Action Plans (RAPs) were developed for each area of concern.

You can view detailed information about each RAP on the EPA’s web site.

EPA’s web site (packed with information).

For an alternative point of view, try this Canadian web site.Now where were we before spring break…

Thermodynamics:The Transfer of Heat

Convection

Conduction

Radiation

Thermodynamics:Heat Engines

A heat engine takes energy in the form of heat, converts some of it to useful work, and discards the rest.

An engine is a device which converts energy into mechanical force or motion.

Thanks to Dr. Bieniek for the picture.

Nuclear power plants are heat engines. The “only” difference between them and “conventional” power plants is that nuclear energy is used to generate the heat.

heat in

work done

“waste” heat out

Now we come to the laws of thermodynamics. Remember Newton's three laws? Everything good comes in threes, right?

The Laws of Thermodynamics:

The First Law

Well, no. There are only two laws of thermodynamics, and we have already heard of the first, which states that "in any closed system, the total energy remains constant, although it may be transformed from one form into another."

Sometimes the flow of heat from high-temperature to low-temperature regions is called the 0th law of thermodynamics. That way you can still have your good things in threes.

An equivalent statement of the first law is "the total energy of the universe is constant."

It sounds pretty simple, but the discovery of the first law has been characterized as one of the greatest achievements of the human mind.

“In any closed system, the total energy remains constant, although it may be transformed from one form into another.”

Remember, the laws of physics are based on centuries of thought, experimentation, theory, successful predictions, more experimentation, and new inventions. The conservation laws are demanded by experiment, by observed symmetries in nature, and by theory.

There are plenty of people who would like to convince you they have overthrown these laws.

These facts exist, so the laws must support them. If you want to disprove the first law of thermodynamics, you had better have an alternative law which explains all the known facts, plus makes successful predictions the first law is incapable of.

What these people neglect to tell you is that if you overthrow these laws, you remove the foundations of a vast collection of observed facts.

There are people who would like to legislate solutions to environmental problems by ignoring physics; these people forget (or neglect to tell you) that you can't legislate the laws of physics.

The first law of thermodynamics says, for example, that you can't make a machine which creates more work than the energy you input into it.

It says that no machine can be more than 100% efficient. (We will see later that the second law puts even lower limits on maximum machine efficiency.)

Another name for a machine which creates energy is a perpetual motion machine of the first kind.

You can’t get more work out than you put energy in.You really can't get something for nothing. Sorry.

Lots of people have "invented" and built perpetual motion machines.

Some of them have been very clever and have fooled experienced and reputable physicists.

In every case where the machine “produced” energy, there was a hidden source of energy which made it look like the machine was producing more energy than it used.

Rube Goldberg didn’t invent perpetual motion machines. His machines just remind me of purported perpetual motion machines.

We have seen how the first law of thermodynamics says you can't get “something” for “nothing.” Next we will learn how the second law of thermodynamics says you can't even get equal amounts of “something” for “something.”

The second law of thermodynamics deals with entropy, so I had better talk about it for a minute. Has anybody heard of entropy? Who can tell me what it is...

The Laws of Thermodynamics:

Entropy

Right now this room is full of oxygen molecules, which all of us are breathing.

The oxygen molecules are in random motion, moving at typical speeds of a few hundred meters per second, bouncing off things like tiny billiard balls and constantly changing direction.

What are the chances that all the oxygen molecules might all of a sudden congregate in the cubic foot of volume at the upper northwest corner of the room?

The link above won’t work on this computer. Here are two other links to on-line molecular motion simulators:

http://www.falstad.com/gas/ http://www2.biglobe.ne.jp/~norimari/science/JavaApp/Mole/e-gas.html

What are the chances that all the oxygen molecules might all of a sudden congregate in the cubic foot of volume at the upper northwest corner of the room? Anybody feel difficulty breathing all of a sudden?

Of course, none of us are worried that all the oxygen molecules are going to "decide" to gather in one corner of the room.

On the other hand, suppose we released a very potent quart of cheap perfume (most of you probably haven't had kids, so you haven't experienced the pleasure of "My Little Pony" perfume) in that same corner of the room.

What would happen?

All the oxygen molecules gathering in one corner of the room is a more ordered situation than all the oxygen molecules moving randomly throughout the room.A quart of perfume in one corner of the room is a more ordered situation than a quart of perfume molecules dispersed throughout the room.

Events which occur spontaneously (all by themselves) result in a decrease of order (in increase of disorder, depending on whether you are a pessimist or an optimist).Events in which order increases cannot occur spontaneously; work must be done to increase order. (Anybody with kids, or adults with messy desks, can understand this.)

Entropy is the physicist's measure of disorder. The greater the entropy of a system, the greater the disorder.If an event occurs spontaneously, entropy increases. If entropy is to be decreased, energy must be expended.

Life is interesting in that it creates small regions of the universe in which order is increased, at the cost of other regions of the universe in which order is decreased.

“What we did: worked …”

Physicists classify processes as reversible and irreversible.

There aren't a lot of truly reversible processes around. Letting a gas expand v e r y s l o w l y in a chamber, slowly enough that its temperature doesn't change, is an example of a reversible process.

An irreversible process would be burning a piece of paper, blowing up a stick of dynamite, or frying an egg.

Things that make processes irreversible: friction heat transfer mass transfer mixing.

Here’s a “movie” of an (almost) reversible process, and an irreversible process. Here’s a web link to the movie. Can you tell which is “forward” and which is “reverse?”

The second law of thermodynamics says that entropy increases in all irreversible processes, and remains constant in all reversible processes, so that the total entropy of a system never decreases.

That sounds very abstract, but it has a number of enormously significant consequences.

Equivalently, it says that the entropy of the universe is always increasing towards a maximum.

You can’t even get out work equal to the energy you spent. Sorry.

“Wasted” energy must be nonzero.

temperature of heat sinkefficiency = 1- .

temperature of heat source

I'm going to hit you with an equation here, but it won't hurt too bad. Starting from the second law of thermodynamics, you can show that the efficiency of an ideal heat engine is

Notice that you can have an efficiency of 1 (100% efficient) only if the temperature of the heat sink (the river, in the case of the power plant) is at absolute zero, or if the heat source (the steam) is at an infinite temperature. Neither of these ideal cases is even remotely practical.

heat in (TH)

work done

“waste” heat (TC)

Worse yet, any real engine will have other places where energy is lost (e.g. friction) so real engines have efficiencies lower than the theoretical best.

H

C

Te = 1-

T

Let's suppose our power plant uses steam (under pressure) at 700 C, which is equal to 973 K. (The equation I wrote down before requires absolute temperature in degrees Kelvin.) That's pretty hot steam.

heat dump

heat source

300Tefficiency = 1- = 1- = .692973T

Let's suppose the power plant dumps waste heat into the river at a temperature of 27 C (or 300 K). That's actually hotter than a free-flowing natural river, but not by a whole lot. Our equation says

If this power plant burns a ton of coal, about 30% is “lost” due to Physics. Another 15% or so is lost due to “friction.” About 7% is lost transmitting the electricity over power lines.We’re lucky if even half of the coal was put to “good” use.

This inefficiency is not due to poor engineering or lack of cleverness; it is a limitation built into nature which we cannot overcome.

In fact, any power plant uses mechanical parts to turn the energy of the steam into work, and all of these mechanical parts are subject to inefficiencies such as friction.This is where clever engineering can help; it can help us approach the theoretical maximum efficiency.

According to the textbook I looked in, a power plant operating at the above temperatures might have an actual efficiency of about 47%. Over half the energy it uses is wasted before it “leaves” the plant!

Let me close by reminding you of the second law of thermodynamics, which says no process is possible whose sole result is the extraction of heat from a reservoir and the conversion of it into useful work.

A machine purported to do just that is called a perpetual motion machine of the second kind; no such machine can be made. The equation for efficiency tells you how much of the energy must be wasted.

A question for you psych. people in this class: what (big, general) things motivate people?

Maybe not the most effective motivator, but rather important.

Those who claim to have invented perpetual motion machines usually claim a conspiracy of scientists or utility companies prevents them from getting their machine accepted.According to US law, all they have to do is plug their machine into the power grid (at the proper phase) and start billing the utility companies.If billions of dollars were to be made, would you neglect to plug your perpetual motion machine into the power grid?

If time permits, and if I can assemble the materials in time, I will do a little demonstration which illustrates convection. It also relates to Newton's laws and mechanics, which we studied earlier...

Convection

Not much happens.

Mixing.

Warm water on top.

Warm water below.

Cold, dense water pulled down by force of gravity.

Warm, less dense water pulled down less by force of gravity.

Warm water on top.

Cold water on top.

Gravity pulls the denser cold water down.

The hot water is displaced “up.”

Eventually, the water temperature becomes uniform throughout.

Be sure to go out after class and tell all your friends that warm air doesn't really rise, but that cold air sinks.

On second thought, maybe just keep your mouths shut. Here are some other illustrations of convection, borrowed from this web page.

boiling water radiator

fridge

Convection is important in nature, too.

Do you suppose we could put a little paddlewheel in the convection current and watch it turn?

Do you suppose we could hook that wheel up to some kind of a generator and generate electricity?

You bet! Some have proposed this as a method of harvesting energy from the sea.

Sure, we could!

Can you think of pros and cons to this method? Who will like it, who will object, and what long-term consequences might it have?