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) [1], 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.
By the end of this module, you should be able to:
To Read | Materials on the course website (Module 2) | |
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To Do | Module 2 Discussion Post Module 2 Discussion Comments Quiz 2 |
Due Wednesday Due Sunday Due Sunday |
If you have any questions, please email your faculty member through Canvas. We will check daily to respond. If your question is one that is relevant to the entire class, we may respond to the entire class rather than individually.
If you have any questions, please post them to the Help Discussion Form. We will check that discussion forum daily to respond. While you are there, feel free to post your own responses if you, too, are able to help out a classmate.
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!
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.
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.
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!
Short 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?
Mistakes in unit conversions really can cost an immense amount of money. We are NOT going to turn this course into a worksheet on unit conversions, and we won’t require you to memorize unit conversions, but we will explain some of the key points next—enough to let you keep your hypothetical job with the power company...and maybe a real job someday.
Words such as energy, work, and power are tossed around in casual conversation but have very careful definitions in engineering and science, and for the people who buy and sell energy. You can think of energy as the ability to do something. Wind up an old-style alarm clock, and the spring has stored some mechanical energy, which is available to move the clock hands and make the ticking sound. Water above a dam has gravitational potential energy and can flow down under gravity, driving a generator to make electricity, or floating your boat to the sea. The chemical bonds in the gasoline in your car have chemical energy, and if you make the gas hot enough with a spark in your engine in the presence of oxygen, the bonds will change and make the car go.
When you are “using” the energy, it is doing work. Pushing you across the country, or moving the clock hands, or moving your boat down the river, require overcoming friction and wind resistance and such. So does using a plow to break the soil and turn it over so you can grow food and lots of other things. How fast you use energy, or how fast you do work, is power. You do some amount of work in climbing the stairs to the next floor, but doing it in 10 seconds requires more power for a shorter time than doing it in 10 hours.
In terms of units, and how you’ll answer your boss about the Quebec contract, energy can be measured in calories. A Big Mac has just over 500 calories, so 4 sandwiches provide just over the 2000 calories that a typical person would eat in a day. Most of the world measures energy in joules rather than calories, and those 4 Big Macs are just over 8 million joules, which is the same as 8 megajoules.
If you were on a starvation diet, you might make those 4 Big Macs last a month—a low-power diet! But if you eat 2000 calories per day and “burn” them inside you to make you go—normal power for a person—that is the same as 8 million joules per day, or roughly 100 joules per second, which is called 100 watts. Amazing as it may seem, all your skills and brilliance and good looks and charm use energy at the same rate as one old incandescent light bulb! Your energy use—your personal power—is a bit higher than 100 watts when you’re up and doing things, and lower when you’re sleeping, but averages out to 100 watts. We don’t usually define a “people power” unit, but 750 watts, or 7.5 people, is a usual definition of 1 horsepower.
So, energy can be measured in calories or joules and is the ability to do something, while power in calories per day or joules per second is how rapidly you do it, and a watt is a shorthand way of saying joules per second. But, suppose you have 10 old-style light bulbs turned on all the time, so you’re using 1000 watts or 1 kilowatt. Each hour, the computer at the power company says you have spent another hour using 1 kilowatt, so they add the price of 1 kilowatt-hour of electricity to your bill. At the end of 24 hours, you are billed for 24 kilowatt-hours. Kilowatt-hours, like calories and joules, provide a way to measure energy. The Quebec company uses joules, you use kilowatt hours, and you’ll keep your job because you know (maybe with some help from the internet) that 1 kilowatt-hour is 3.6 million joules, so those Québécois are not going to beat you in a deal!
In case you feel a sudden urge to actually do calculations with these, you might recall that the calorie you eat is sometimes also written as a capital-C Calorie, and is the energy to raise 1 kilogram of water by 1 degree C, distinguished from a calorie that is written with a lower-case c and is the energy to raise 1 gram of water by 1 degree C. So when we read about food calories, we are really talking about kilocalories. This is another reason why most of the world uses joules.
You should also know that there are many more ways to measure these things, which you do not need to learn now, but which you should know exist. People often use British Thermal Units, or BTU's, for energy, and BTU's per hour for power, but occasionally they get sloppy and say “BTU” when they mean “BTU per hour”. Or, they get lazy and say that one quadrillion BTU's is a “quad” and just quit talking about BTU's. People who sell natural gas have figured out how many BTU's, or joules, or calories, can be obtained by burning a particular amount of typical natural gas, and how much space that gas occupies at standard temperature and pressure, so they may measure energy in cubic feet of gas, or cubic meters of gas, even though they know that this depends on temperature and pressure and the particular gas. Barrels of oil can be used the same way. And, it goes on from here—refrigeration workers in the US talk about power in terms of “tons of cooling” linked to the power needed to freeze a ton of water in a day (one ton of cooling is approximately 3510 watts).
Now, we hope it is obvious that unless you are planning to work in cooling, or you have rather strange friends you would like to impress, it is probably not a good idea to clog your brain with the conversion factor between watts and tons of cooling! But you should know that a few fundamental ideas such as energy and power have been made to look very complicated by having a lot of names and units. And you also should know that many jobs you might be hired for will require you to figure out: 1) how things traditionally have been measured; and 2) how to convert to what other people are doing in their jobs. And if you can’t do that reliably, there is a high chance that you will be fired!
Short 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.
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 [2]. 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….
Energy use in the US is dominated by fossil fuels—oil (or more formally, petroleum), gas (or more formally, natural gas), and coal (which is generally just called coal). Recently, fossil fuels have been totaling about 85% of energy sales in the US (and more-or-less 85% worldwide), with the rest of US use split more-or-less equally between nuclear and renewables. (In 2010, the US Energy Information Administration gave US energy supply as Oil 37%; Gas 26%; Coal 21%; Nuclear 8%; Renewables 8%. This was used to move us around (transportation 28%), to build things (industrial use 20%), to heat and cool houses (residential 11%) and to power our plugged-in gizmos (electricity 40%).
We’ll revisit these issues later. US usage per person is a little smaller than some countries, but (much) larger than many others. Per person, the world averages roughly 1/4 of US use. Most of the world's economy is dominantly fossil-fueled with people often getting about 85% of their energy from fossil fuels as in the US, and energy is often about 10% of the economy.
In the previous section, we learned that the average person in the US uses ~10,000 watts of energy while producing only 100 watts from the food they eat. If average world energy use is about 1/4 of that in the US, and assuming all people produce about the same amount of energy from the food they eat, do people worldwide create as much energy from eating food as they use in their daily lives?
Click for answer.
For now, though, it should be evident that if we spend 10% of our money on energy, it impacts everything—jobs and security and environment and more. As we saw in last week's Discussion, there are great options for making money and saving money by doing things better in the energy business. But, over the last few decades, we actually have doubled the amount of economic activity squeezed out of each barrel of oil or ton of coal—bright people have been working on this, and making or saving much more money might take a lot of effort or some new inventions.
Perhaps most importantly, the current system is grossly unsustainable. As we will see in upcoming content, the store of fossil fuels in the Earth is limited, and we are removing them much more rapidly than nature makes new ones. With essentially everything we do relying on energy use and 85% of the energy system relying on unsustainable fossil fuels, a lot of things will need to change.
Earth: The Operators' Manual
After completing your Discussion Assignment, don't forget to log into Canvas and take the Module 2 Quiz. If you didn't answer the Learning Checkpoint questions, take a few minutes to complete them now. They will help your study for the quiz and you may even see a few of those question on the quiz!
Compare energy consumption in the U.S. to that in other countries. Find the total per capita energy use for a country of your choosing. Is it more or less than that in the US? Is it growing at the same rate? Why might this be?
Throughout this module, most of the facts and figures about energy have been for the United States. Of course, the entire world uses energy in varying capacities. Take a moment to take a look at what is happening outside the US. If you live in another country, or if your family is from another country, what is the energy situation there and how is it different from the US? Perhaps you have visited another country or heard something interesting about energy production or consumption elsewhere in the world.
As a starting point, go to the U.S. Energy Information Administration website [4] and look at per capita energy consumption in the US vs. your country of choice between 1980 and 2015. Use the DATA pull-down menu to select "Primary Energy Consumption" then click on the Time Series icon below the map. Next, click on the Select Data icon and in the window that pops up, select Energy Intensity in item 2 and Population in item 4 and then click on View Data at the bottom of this window. Then click on the Select Countries icon and another window will pop up -- here, click on All Countries and you will see a list of all the countries, then click View at the bottom of this window. Scroll down below the graph and you will see a list of all the countries -- if you click on the graph icon to the right of a country, the data will appear on the graph; click on another country and its data will also appear.
If the above link does not work, try an alternative source, IEA Energy Atlas [5].Make sure that you select TPES/Population (which is tons of oil equivalent per person), then scroll down to the very bottom of the page, where you can make a graph that compares your country with the United States.
How does the per capita use in 2015 compare with the US and your country? How does the change in use from 1980 to 2015 compare? Given what you know about the country, what factors do you think might contribute to differences in energy use?
Next, find one fact about energy consumption or production in the country you have chosen that you think is especially interesting, and tell us why you think your country has this particular feature. For example, oil use may be increasing as industry grows in a developing nation. Or wind energy may be growing rapidly because you have a long and windy coastline. Maybe you live near a volcano and get all your power from geothermal energy.
Your discussion post should be 150-200 words and should include the name of the country you have chosen to research as well as numerical data comparing energy consumption in the US to that in your country of choice. Make sure the questions posed above are answered completely. Your original post must be submitted by Wednesday. In addition, you are required to comment on one of your peers' posts by Sunday. You can comment on as many posts as you like, but please make your first comment to a post that does not have any posts yet. Once you have an idea of what you want your post to be, go to the course discussion for your campus and create a new post.
The discussion post is worth a total of 20 points. The comment is worth an additional 5 points.
Description | Possible Points |
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states name of country and includes numerical data (with units!) for energy consumption in US and chosen country | 5 |
compares current or recent usage (2010 is close enough) and change in usage (1980-2010) for US and country of choice | 5 |
identifies at least one reason why energy use in chosen country might differ from that in US | 5 |
includes one interesting fact about energy use or production that is particular to country of choice | 5 |
well-reasoned comment on someone else's post | 5 |
We love the good things we get from using energy, and we use a lot of it. When we “use” energy, it doesn’t disappear, but it is changed to a form that is less useful, and eventually, it becomes totally useless to us. So, we spend a lot of effort into finding sources of concentrated energy that we can use. How rapidly we use energy is called power. You could use most of the energy in your food to sprint down a racetrack, generate high power, and then rest up afterward with low power, or you could use the same amount of energy in the same amount of time by walking steadily with intermediate power output. We measure energy in joules or calories or kilowatt-hours, and power in watts or calories per day or in other ways. Food burning inside us averages about 100 watts, but in the US the energy use outside is more than 100 times larger, and almost everyone almost everywhere uses far more energy outside than inside—the global average is roughly 25 times more energy use outside than inside. And, for most of the world, the energy used is primarily fossil fuels—85% in the US, and similar for most places. Typically, this is about 10% of the economy. So, we spend a lot of money to get good things from energy.
You have reached the end of Module 2! Double-check the Module Roadmap to make sure you have completed all of the activities listed there before you begin Module 3.
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.
We 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!
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.
Links
[1] https://www.nist.gov/pml/owm/metric-si/si-units#:~:text=The%20International%20System%20of%20Units,globe%20as%20World%20Metrology%20Day%20.
[2] http://www.eia.gov/
[3] http://www.eia.gov/totalenergy/data/annual/index.cfm#summary
[4] http://www.eia.gov/cfapps/ipdbproject/iedindex3.cfm?tid=44&pid=44&aid=2&cid=regions&syid=1980&eyid=2010&unit=MBTUPP
[5] http://energyatlas.iea.org/#!/tellmap/1378539487