Module 2: What is Energy?
Module 2: What is Energy?Module 2: Overview
Why take a course on energy? With over $1 trillion spent per year on energy in the US alone, the knowledge you gain from this course may help you in your career and your everyday life. And because we currently rely on a completely unsustainable energy system that must change, your knowledge may help the long-term health of civilization. Plus, believe it or not, the subject really is interesting!
In this module, we’ll go over some of the basics—how do we talk about energy, what is it, how much of it do we use, and such. Back in the late 1990s, NASA lost a $125 million Mars orbiter because some members of the mission team were figuring out its location using metric units (e.g., meters, centimeters, liters) also called the International System of Units (SI), others were using English units (e.g., feet, inches, ounces); the different groups didn’t recognize this and convert properly — a very expensive mistake! The situation with energy is actually more confusing than that. So, bear with us, and we’ll try to start off in the right direction.
Goals and Objectives
Goals and ObjectivesModule 2 Goals and Objectives
Goals:
- Recognize the natural and human-driven systems and processes that produce energy and affect the environment
- Explain scientific concepts in language non-scientists can understand
- Find reliable sources of information on the internet
By the end of this module, you should be able to:
- Recall that using energy doesn’t make it go away, it is just converted into a less useful form
- Recognize the many units of energy and power
- Show that the amount of energy used by people around the world is much larger than the 100 watts inside most people converted from food
- Recall that around 85% of the energy we use is derived from fossil fuels
- Analyze energy use and production in a country other than the United States
Three Examples
Three ExamplesEnergy is Forever, but Useful Energy Is Not
Physicists have found that in our normal lives, energy is neither created nor destroyed — it is conserved. But as energy is used, it is changed from a concentrated, useful form to a spread-out, less-useful form, eventually becoming useless to us. To learn what Einstein has to say, read the Enrichment on the next page. But first, let's look at three examples.
Want to know more?
If you are worried about Einstein and atomic bombs and want to learn more about it, read the Enrichment called Einstein's Special Relativity Theory E=mc2!
Example 1: Potato Chips
Throw a bag of potato chips on the floor, and stomp on it. Keep stomping until all of the chips are reduced to dust. Then, on a really windy day, go to the top of a hill and throw the dust as high as you can.
There are still calories in that potato-chip dust. If you could somehow re-bag your chip dust, you could eat it and then go about your business, fueled by the energy stored in the potato chips. In the real world, bacteria are going to get that energy because it would take you much more energy to gather up the potato-chip dust than you could ever get by eating it, even if you wanted to.
Energy itself is a little like your potato chips. Energy doesn’t disappear when you use it to do something you want, but the energy is changed to a less useful form until eventually, it is completely useless to you. If yu eat the potato chips, your body will digest them and turn them into fuel that keeps your body going, which in part means generating heat to keep your body temperature at an average of 98.6°F, and then some of that heat is emitted from your body, traveling out in the form of infrared radiation, which is a form of energy. So the energy stored in the chips has been put to use and has changed from chemical energy in the chips to thermal energy that your body emits. And that thermal energy gets dispersed and is not really useful anymore, although it is conserved.
Video: Potato Chip (2:57)
Potato Chip
DR. RICHARD ALLEY: These are potato chips-- crisps, in England. The chemicals in here are a concentrated source of energy that my body could store for later, or it could burn now to power me to do things that I think I need to do, like mow the lawn. And this is gasoline. The chemicals in here are a concentrated store of energy that I can use to power my lawnmower, to help me mow the lawn.
So if I were to take my chips, dump them on the driveway, and stomp on them with my big boots, the chemicals, the energy, would still be in there, but it just wouldn't be as useful to me. Especially if I took my lawnmower—
And I spread them all over everything.
So the stuff is there, the energy is there, but I've made it no longer useful. In exactly the same way, there's now less gasoline in the mower than there used to be. I have burned it. The stuff has gone into water vapor and CO2 in the air. And the energy, a little bit of it, made noise to annoy the neighbors. But eventually, that just heated up the surroundings. And a lot of went right into heat, so if you touched the wrong piece on this mower, you would burn yourself now.
So what we see in the real world, normal times, stuff and energy are not lost or made, but they're changed from one type to another. And with energy, we tend to change it from useful types to things that are not as useful, and eventually to heat that spreads out and does no good for us. A lot of the history of humanity has been finding concentrated sources of energy and trying to get useful things out of it as we change it into useless heat that spreads around the world. That may give you an idea that we'll come back to later.
If we were using sun or wind or hydropower to run an electric mower, I'd be making a lot less noise, I'd be making a lot less heat. I'd be using the energy I bought for what I wanted, rather than wasting it.
Example 2: Gas in the Car
The chemical energy in a full gas tank in your car is enough for you to drive 400 miles or so. As you burn the gas, the muffler gets hot, and you warm the air and the tires and the road a little—you are turning the gasoline’s energy into heat. You could put a little thermoelectric device in your tailpipe and generate enough electricity to run your music player, or you could blow some of the hot air through the heater to keep you warm on a cold winter day—the heat can still be useful—but you’re using lots more energy to move the car than you’ll ever get back. After you stop the car and the muffler cools off, the heat energy has been spread out into the air and is being radiated away to space — if you had a thermal camera, you could take a picture of it. A satellite can even see the heat going to space, and make a map of how warm or cold the Earth is, so there is still some use in that energy...but not much. And eventually, the energy will spread uniformly across the universe and be completely useless.
Example 3: Bungee Jumping
While Dr. Alley was in New Zealand filming footage for Earth: The Operators' Manual, he took the opportunity to test another use of energy (his energy) by bungee jumping. He gained potential energy (the ability to fall down fast) by climbing up to the top of the jump. That is turned into kinetic energy (motion, the ability to collide with things) by jumping off. After the thrilling few seconds of the jump, all that energy ends up heating the surroundings a bit and is no longer useful.
The key piece of knowledge to take away from these three examples of how energy is changed from a useful to a non-useful form is: if you want to keep doing things, you need new sources of concentrated energy. That’s what this course is about!
Powering the Big Units
Powering the Big UnitsShort Version: Energy is the ability to do something, and is measured in joules or calories or kilowatt-hours or in other ways. Power is how fast you do it, and is measured in watts or horsepower or in other ways. Your 2000-calories-per-day diet is the same as a single 100-watt light bulb burning all day. Let's take a closer look!
Friendlier but Longer Version: Suppose that you are an employee at a Pennsylvania power company. Your customers buy a lot of kilowatt-hours of electricity to run their microwave ovens and music players, but your power plant needs to be turned off for maintenance. Your boss tells you to buy some power from a hydroelectric company in Quebec, but they don't have any kilowatt-hours for sale -- all they offer are megajoules. What do you do?
Energy and the US Economy
Energy and the US EconomyShort Version: Energy is 10% of the US economy—over \$1 trillion per year, or \$4000 per year for each person, with roughly \$1000 of that leaving the country, to supply the average US resident with more than 100 times more energy than they use internally. About 85% of the energy used is from fossil fuels, which are being burned much faster than nature makes more.
Friendlier but Longer Version: During the course, we’ll take a look at the big sources of energy, the big issues in energy use, the “why you might care” and “what it means to you” questions. For now, a few more-or-less connected numbers and graphs may be useful. This course is not about having you memorize numbers, but you should be aware of magnitudes—which things are really big and matter a lot, versus those that are small and can be safely ignored (unless you’re the wonk on this topic and need to know everything!).
As you just saw, the food you burn inside powers you at the same rate, on average, as a bright old-style light bulb (100 watts) that is turned on. But, the food may have been cooked, after it was shipped to you in a refrigerated truck after it was harvested by a corn-picker or combine from a field that first was plowed by a tractor. The plowing and harvesting and trucking and refrigerating and cooking all required energy. You probably are reading this on an electric-powered computer, in a room that is heated in winter and cooled in summer using energy. If there is glass on the computer screen, it started out as sand, which was melted using energy. Aluminum or iron or other metals were smelted from ores, using energy.
Video: Energy Use (1:09)
Energy use increases as economies grow. The plots show energy intensity (how much energy is used per dollar of economic activity) and economic activity (dollars per person per year), plotted against total energy use, for the different continents. Bigger economies use more energy. There is no strong relation between how big an economy is and how efficiently it uses energy, but a slight suggestion that bigger economies are more efficient.
DR. RICHARD ALLEY: These are a couple of plots showing some information about human use of energy and economy. Use of energy per person per year is on the bottom-- zero, not using any over to using a huge amount. And this amount is about 100 times more energy used outside the person than inside. And what you'll notice is this is economic activity-- how big the economy is, how many dollars per person per year. And poor people don't use much energy, and rich people use a lot of energy. Now, you might first think that that means that rich people are just wasteful. But what you see above is how much energy is needed to generate \$1 of economic activity, and there just isn't much relationship there. So, it's not that rich people are wasting more energy. They get as much activity out of a barrel of oil as poor people do. They just generate way more economy. And so, you use more energy when you're rich, basically.
Source: Data from US Energy Information Agency, for 2006; plot prepared by Richard Alley.
You get the idea. And, if you add up all that energy, there is a lot of it. The total energy use in the US economy, divided by the number of people, comes to a bit over 10,000 watts per person—all together, everything that is going on around you to take care of you involves more than 100 times the energy use inside of you. You don’t really have more than 100 incandescent bulbs burning all the time to take care of you, but all the plowing and harvesting and trucking and refrigerating and cooling and smelting and melting and heating and cooling and … that do take care of you are using energy at the same rate as more than 100 old light bulbs, or 100 of you.
You might imagine that you have 100 energy “serfs” doing your bidding… but if you actually had 100 serfs to do your bidding, they would spend most of their effort taking care of themselves and staying alive rather than doing for you. Plus, there is no way that those serfs could actually pick up your car and run down the highway at 65 miles per hour (100 km per hour)!
This much energy doesn’t come cheaply, though. Energy costs are roughly one-tenth of the entire US economy. That comes to about $1 trillion per year recently, or about $4000 per person per year, with roughly $1000 of that spent outside the US to pay for energy imports. (These numbers bounce around some from year to year; you can get updates at the US Energy Information Administration. So, each year, a US resident is sending ~$1000 to people outside the US, primarily to pay for gasoline. Those people overseas may use those dollars to buy US-made products, or to visit the US, or to buy US companies, or to buy camels or classic paintings, or to buy bullets, or in other ways—once the money is sent over the border, it is theirs….
Enrichments
EnrichmentsOptional Enrichments
Use the links to go to the enrichments. Please note that these materials are not required and will not be covered in the assessments, but they are interesting and will enrich your overall understanding.
Einstein's Special Relativity Theory
Einstein's Special Relativity TheoryWe normally think that the world contains matter-stuff-and energy (the ability to get the stuff to do something). And we often measure how much stuff we have by its mass. (Weight is the mass multiplied by the acceleration of gravity.) A real physicist would remind you, however, that mass and energy are different aspects of something more fundamental.
Einstein’s famous formula says that the energy content of something, E, is equivalent to its rest mass, m, multiplied by the square of the speed of light in a vacuum, c2. Because c is so large, a reaction that converts a little bit of mass can produce a lot of energy that is radiated away, as in an atomic bomb, for example.
The numbers are really wonderfully large. If you could somehow make an Einstein reactor to convert the matter in the food you eat directly to energy, just 1 gram (one-fifth of a teaspoon of water) would be enough to supply your 2000-calories-per-day diet for 30,000 years!
Laws of Thermodynamics
Suppose you don’t have an “Einstein reactor”, so you’re working in the ordinary world, where any changes between rest mass and energy involve too little mass to be measured. Then, as described in the main text, energy is neither created nor destroyed, but it is changed from one form to another. This is often called the First Law of Thermodynamics, and also can be written that the change of the energy in a system is the amount of heat added to it minus the amount of work it does on its surroundings.
The first law of thermodynamics, by itself, might leave you thinking that after you burn the gasoline to move your car to drive to Grandma’s house, heating the surroundings, you could just collect the heat and the carbon dioxide and the water from your tailpipe, put them all back together again, put that gas back in your tank, and drive home. The Second Law of Thermodynamics says that you will fail; it is possible to use the heat to recombine things to make more gasoline, but you’ll never get as much energy back into the gasoline as you started with. “Disorder”, or “entropy”, increases, and the concentrated energy that is useful to us becomes spread out and no longer useful.
Physicists often discuss a zeroth law of thermodynamics, which says that if two things are in thermal equilibrium with each other (not having a net flow of heat from one to the other), they are in equilibrium with a third. This leads to a definition of temperature, and other useful things. And, there is a third law of thermodynamics which says that you can’t actually cool something to absolute zero, the point at which a perfect crystal would have zero entropy. These can be approximated as (this is often attributed to the British thinker C.P. Snow): You must play the game, but you can’t win, you could break even on a really cold day, but it never gets that cold.