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Energy Tutorial:
What is energy?
Where do we get it?
What are the consequences?
Is it conserved?

What is Energy?
One way to define energy is by observation. If you see something that doesn't happen on its own, then there must be some energy being expended. For example, cars don't go up hill on their own, so there must be some energy getting used. Coming downhill, however, we could see that happening without any energy being used.
Like the car going up hill, anything that gets lifted against gravity requires some energy. Fortunately, this energy has the potential to be used again.  For example, the skiers' bodies are given potential energy as the are lifted towards the top of the mountain.  They will change that potential energy to kinetic energy as they ski down the slopes.  We sense this energy when we are lifted up to high places.  We know we can fall and turn that potential energy into broken bones.
We can think of just two types of energy, one doing work, and the other waiting to do work.

Freedom Train at Houston Union Station, February 1976 - photo © Gary Morris (Used with Permission)
When it's doing work, we see it pushing or pulling, glowing, or changing the temperature. This train is using energy in three ways because it's pulling cars, heating up the surrounding air, and giving off light.  "Glowing" means giving off any kind of light in the electromagnetic spectrum. That's radio waves, infrared (heat) light, visible light, ultraviolet light, and xrays.  Making sound is also energy that is pushing on the air and eardrums. 
Energy that is waiting to do work (has to the potential for work) is called potential energy and is recognized in 3 ways:
    1) It sits above ground level
On the left is a pile driver. A weight (the driver) is lifted up to the top of the rig. The weight now has potential energy. As it falls the potential energy becomes kinetic energy (moving energy). When it strikes the post (pile/piling) at the bottom, the kinetic energy is used to drive the post farther into the ground (do work). It's a smart way to deliver a lot of force. Wrestlers use the pile driver maneuver by lifting the opponent and letting gravity do the work as the opponent falls to the mat head first. On the right is Hoover dam. Lake Mead is held back by the dam. Lake Mead sits higher than the ground below the dam. This means the water in the lake has a lot of potential energy. This energy is tapped when water is allowed to flow downhill (turns to kinetic energy) and then does work by spinning turbines that spin magnets that push on electrons (crowds them together) to make voltage and electrical energy.   The work happens when the magnets push on the electrons that have a resistance of getting crowded together.
Energy is potential energy if: 2) Something is compressed or stretched in someway
A set mousetrap has a spring that has been compressed (or stretched), and it's sitting there ready to convert this potential energy to kinetic energy as the wire trap flips over to the other side.

A tank of compressed air also possesses potential energy. If an air tool is attached that potential energy is used to push a piston that makes the air tool mechanism spin or vibrate.


3) Kinetic energy is the energy of something that moving. However, if that moving object is not pushing anything (like a spinning flywheel, a swinging hammer, or meteor flying through space), then this energy is just waiting to do work. So this energy is similar to potential energy yet it's not normally classified as potential energy. When these moving objects start to push on something, then they do work. Again, when that object moves freely then the kinetic energy is waiting to do work. It's like potential energy in that sense that it has the potential to do work but hasn't done it yet. Again, when the moving objectg pushes on something and gets it to move. Then it's becomes work energy, which is a force times the distance that force is applied.

Chemical energy is a type of potential energy.  The diesel in the train above stores chemical energy.  It's similar to raising objects against gravity (like the pile driver) except instead of moving objects against the attraction of gravity, it is moving objects against the attraction of plus and minus charges. To illustrate this, let's look at the simplest of elements, hydrogen....

The hydrogen atom consists of one proton (+) and one electron (-). The proton sits in the center (nucleus) of the atom. The proton is 2,000 times heavier than the electron. The electron is lightweight and very mobile. The diagram shows the electron as a sphere orbiting the nucleus. This is a simplistic view of an electron. Electrons are more cloud-like than ball-like.  If an electron is moved farther away from the proton it takes energy because they are attracted to each other (like gravity). The farther away the electron has been moved away from the proton, the more energy it takes, and the more potential energy stored in the electron. When the electron drops back closer to the proton, it will convert that potential energy to light energy. The light energy can be in the form of infrared, visible, ultraviolet, or even xray light.
Chemical energy is stored in fuels like methane (natural gas) and gasoline. Let's see how methane combining with oxygen (combustion) gives up this type of potential energy.
When methane collides with oxygen at high speeds (caused by flame or spark), there's a rearrangement of the atoms. Two of the oxygen atoms will combine with the four hydrogen (H) atoms to form two water molecules (H2O). The other two oxygen atoms will combine with methane's carbon atom to form carbon dioxide. Why does this give off energy?

Below is the same diagram as above, except all of the protons and electrons that hydrogen, carbon, and oxygen have are shown. Hydrogen has one proton and one electron. Carbon has six protons and six electrons. Oxygen has 8 protons and 8 electrons. Remember the electrons are all being pulled on by the protons (kind of like Earth pulling on objects on the Earth).

The reason energy is released during rearrangement is that overall, the electrons are closer to the protons than they were originally. Remember when the electron on the hydrogen atom goes from farther away to closer, energy is released? Same thing is happening here except several electrons and several protons are involved. This "moving" closer to the nucleus means that some of the potential energy gets converted to light. The light is the visible light you see in the picture plus a great deal of infrared light, which is the heat you feel radiating from the flame.  So chemical reactions are happening because electrons are finding a way to get closer to protons in other atoms.  Oxygen is equivalent to a hole. Electrons from other atoms will "fall into" the orbit of oxygen releasing energy.  That's why oxygen is used to burn things.
Where do we get energy?
Above, you saw pictures of Lake Mead, a locomotive, and a weight lifter. But where did the energy come from that gave the water in Lake Mead the potential energy to generate electricity at the dam? Where did the locomotive get the diesel to power its engines? Where did the weight lifter get his food and the calories to lift the barbell?
Our Sun is the ultimate source of energy that we use here on Earth. The rain that filled Lake Mead came from solar energy evaporating water from the oceans. The diesel for the train came from plants that grew with the Sun's energy and eventually became petroleum. The weight lifter got his calories from meat and plants. The plants got the energy from the Sun, and the meat came from animals that ate plants that got energy from the Sun.
The below picture shows the Sun and Earth and the distance between them to proper scale. If a viewer is far enough back to see the Sun and Earth together, the Sun on the left is visible, but the Earth appears as another dot against the stars in the background. The temperature of space is colder than 400 degrees Fahrenheit below zero. Without the Sun, not only would the Earth's oceans freeze solid, the air in the atmosphere would freeze solid as well.
Considering the distance and relative small size of Earth, it's surprising that we get so much energy from the sun. Fortunately...

The Sun radiates huge amounts of energy in the form of visible light, infrared light (heat light), ultraviolet, and X-rays. Earth intercepts less than one trillionth of this energy. In other words, the Sun puts out enough energy to satisfy 2,000,000,000,000 (2 trillion) Earths.

The picture on the left was taken from the surface of Mars. Earth is seen as a small dot. Mars is about 1 and a half times the distance Earth is from the Sun, which means Mars get less than half the energy from the Sun than Earth does. The polar ice caps of Mars are made from "dry ice" (frozen carbon dioxide) not water ice.
Even though the Sun is the original source of energy, we use different forms of energy that was made possible by the Sun. They are the following:
FOSSIL FUELS: Fossil fuels get their name because they formed from microscopic plants millions of years ago (see pic below). Fossil fuels include natural gas, coal, and the fractions of petroleum such as gasoline, oil, diesel fuel, propane, butane, and tar. Nature has taken 60 to 300 million years to make these fuels, but we might use them up in 17 to 70 years from now, depending on future consumption.
Wind power is a growing source of renewable energy. Fossil fuels are not renewable (unless we can wait 100 million years). But wind power renews itself every day as the Sun energy creates uneven heating and wind is produced. California has been using wind power for quite awhile. Arizona will start its first wind farm this year near the northeastern town of St. Johns. I have a trailer near there, and will vouch for the high winds that come through there. Many of my neighbors use wind generators.

NUCLEAR POWER makes up a small fraction of the power in the US; however, the Palo Verde nuclear plant near Phoenix, is responsible for a large percent of Phoenix's electrical power.

SOLAR ENERGY captured with photovoltaic cells (solar cells). Photovoltaic gets its name because the energy of light (photo) is used to create voltage (voltaic). Photovoltaic cells offer a simple way to get electricity, at least DC (direct current) electricity used in charging batteries. The problem with photovoltaic cells is that they are expensive. It would take three $150 photovoltaic panels to operate the light bulb in your refrigerator. I remember 25 years ago when engineers were promising a big drop in solar cell prices was "just around the corner." Well, I'm still waiting. Photovoltaic cells also only convert about 15% of the sunlight to electricity.
Another approach of using the Sun's energy is to focus the heat from the Sun (infrared light) onto a tube filled with oil. The heated oil is then pumped to an adjacent generating plant that uses the heat to make steam, which then pushes on turbines hooked to electric generators. The polished metal reflectors are cheaper than photovoltaic cells. Even though these panels are fairly simple, you must have steam-powered turbines and electrical generators attached to these collectors.
When done on a large scale, thousands or millions of watts of electricity can be generated from the free energy of the Sun. Even though the energy is free from the Sun, it takes about 20 to 30 years to recover the cost of setting up a solar power station. But one good thing about solar is that in hot climates it produces the most energy at the time it is needed the most, like for air conditioning.
Passive Solar Heating. We should also include passive solar heating. The panels are not photovoltaic cells; they are just black metal behind panes of glass. Air or water passes over the dark metal backing that gets hot from the Sun. The hot air or hot water is used to heat the home or to assist the hot water heater. They are relatively cheap to purchase and install. The downside, is that they are just for the home they are attached to. This heat energy can't be distributed to other places.
Animal Power: Lest we forget, for the majority of mankind's history, the source of power for the chores we had to do was our own body's power plus maybe that of an animal. This was pretty much the limit of our energy consumption. Cooking was done with wood or animal dung.
PonyPower vs. HorsePower: Before the days of machine power, mines used ponies to pull carts of coal or ores or to turn pulleys to lift the coal or ore to the surface. Ponies could lift 220 lbs 100 feet in about a minute. Energy can be defined as force times distance. So here the force to overcome is 220 lbs, and the distance is 100 feet. So the energy is 220lbs x 100 ft = 22,000 ft-lbs. Power is energy consumption within a set amount of time. Here it would be 22,000 ft-lbs per minute. James Watt, the inventor of the new steam engine wanted his engines compared to power of horses, which people were accustomed to.
James Watt knew the power of ponies was about 22,000 ft-lbs per minute. He figured a full-size horse would be about 50% stronger meaning it could lift 330 lbs 100 feet per minute (33,000 ft-lbs. per min). So that became the definition of one horsepower. A ten horsepower steam engine could do the lifting of 10 horses (or 15 ponies).
Human Power: A friend of mine, Paul Walters, was hired to be a bicyclist at the Mountain Dew Amp drink event at SuperBowl 42.  They had forty-two bicyclists pedal for 12 hours per day for total of four days.
Human Power:   Each bike had their rear tire in contact with a generator. So as the bicyclist pedaled they produced electricity.

AMP Drink Power: The purpose of the event is to show all these bicyclist getting energy from guzzling the high sugar, high caffeine, high herbal stimulant liquid. All this to provide power for the pregame show. What a great idea...

Human to Electrical Power: Large banks of batteries captured all of this energy from the 42 bicyclists pedaling 12 hours a day for 4 days.

Cash in the Power: At the end of 4 days and hundreds of Amp drinks, a meter had kept track of the total amount of energy generated. Remember, it amounted to 42 athletic bicyclists pedally 12 hours a day for four days. That multiplies out to be equivalent to 2,016 hours of one bicyclist pedalling.

The electric meter reads 38 kilowatt-hours, which can be interpreted as 38 kilowatts for one hour (like an air conditioner running for one hour) or 1 kilowatt (like a toaster) running for 38 hours. At a cost of about 8 cents per kilowatt-hour, all of this effort produced only 3 dollars of electricity! Yes, only 3 dollars of electricity. This either means that electricity is terribly cheap or that we humans are very weak power sources.

What scares me is if we had to depend on our own legs to create electricity, we are in big trouble. Look at how many watts we can maintain. 38 kilowatt-hours = 38,000 watt-hours. Divide this by 2,016 hours of bicycling, we get about 19 watts. In other words, if we had a athletic bicyclist pedalling away all day, we could only operate electronic devices with 19 watts or less. We would have to have 5 bicyclists just to turn on one 100 watt bulb. So without alternative power, our society would quickly revert back to the days of horse drawn carriages and horse powered everything.

What are the consequences of using energy?

The positive consequence is that we have the energy to make the products we want, travel to where we want, keep ourselves warm or cool, and to power all of the appliances and devices we like in our lives.

The negative consequences can be categorized as inescapable consequences and unfortunate consequences.

INESCAPABLE CONSEQUENCES: The laws of physics cannot be broken. One such law states the impossibility of ever making a perpetual motion machine, which is a machine that does work without any extra energy going into it. In the beginning of the industrial revolution, attentioned focused on the efficiency of machines. Factory owners wanted machines that could either provide work without added energy or at least do work with 100% efficiency. The result of the research was that neither was possible.

INESCAPABLE CONSEQUENCES: The picture on the left is a perpetual motion design. The water in the upper trough pours out on the water wheel on the right. The water wheel turns and the craftsman uses the left wheel for grinding. The tilted corkscrew apparatus is called the Archimedes screw which has the ability to raise water if the screw turns. The water wheel is suppose to provide power for the grinding wheel and the Archimedes screw that will replenish the water to the upper trough. Like all Perpetual Motion Designs, the flaw is that energy gets wasted as heat and there's never enough energy to keep the machine moving. In this example, the falling water will not have enough energy to turn wheels and gears and also pump the same amount of water back into the trough. The friction of the gears, water stirring, and water flowing will turn the potential energy of the raise water into heat.
INESCAPABLE CONSEQUENCES: Energy lost to heat is the final outcome of most anything we do with energy. Let's examine the above collage. The locomotive's purpose is to pull railroad cars from one place to another. However, nearly all of the energy it consumes goes to creating heat rather than moving the cargo. The steam engine or gas engine gets its power by heating a gas which expands and pushes on pistons which turns the wheels. The hot gas is then released (exhausted) so the pistons can return to their original position. The heat energy in the gas is now lost to the environment and no longer available to produce motion.

The weight lifter gets calories from food for energy to lift weight and maintain the body's metabolisum. Only about 20% of the calories gets used by the body, the rest is lost to heat that escapes to the surrounding air. Even the energy in the raised weight will get lost when it hits the floor and warms the spot on the floor where it hits.

Electricity turns a piston in the air compressor to compress the air. The air gets quite hot as it has its molecules pushed closer. This heat energy could provide additional potential energy and pressure. However, the heat quickly dissipates through the metal walls of the compressor and is lost.

The wind generators get energy from the wind. However as the propellors turn, some energy is lost by friction of the bearings. As it generates electricity the friction of electrons travelling through the wires produces heat, which reduces the efficiency of the generator.

In other words, whenever we use energy, most, if not all, will be lost as heat that will no longer be available for doing useful work.

Losing so much energy to wasteful heat is depressing, but another law of physics is even more depressing...
If your life seems more chaotic as time goes by, don't feel alone. All of the universe is experiencing the same problem. When energy is used, more disorder (chaos) is created. In physics this is called "entropy," a measure of disorder often resulting from heat.
For example, the atoms of carbon and hydrogen in gasoline are lined up neatly in chains. After energy is released, the atoms are scattered and randomized. In other words, car exhaust has much higher entropy (disorder) than does gasoline and oxygen. In part because exhaust is a gas, which is bouncing in all directions. The extra heat causes even more random movements.
A warm homogenous soup. Because of this law which states all natural events lead to ever increasing disorder and wasted heat, a prediction of how the universe will end has been made. When the universe reaches uniform temperature and maximum randomness, we can no longer extract energy to do work or to survive. Don't worry. If true, it's still billions of years from now.
CONSERVATION OF ENERGY: Another inescapable consequence of energy is that energy is conserved. In other words, it doesn't go away, it just changes form. The simplest change of form to see is the pendulum. At the top of the pendulum swing, the ball comes to rest momentarily. At that point it has no kinetic energy, but it is at the maxium height, so it has the maximum potential energy. At the bottom of the swing, it is moving the fastest (highest kinetic energy) but has the lowest potential energy. So the energy transforms from one to the other continually.

Friction convert Energies to Heat Energy:
In theory a pendulum should swing forever, but we all know that it will slow down and stop. That's because the movement of the pendulum is knocking against air molecules. The oxygen and nitrogen molecules in the air move about 1,000 miles per hour; however, when they strike the pendulum ball that's moving about 10 miles an hour, the air molecules get a boost of speed increase to about 1,010 miles per hour. So some of the kinetic energy of the pendulum is getting transferred to the air molecules. This extra speed in the air molecules actually means the air is now a little hotter. Also, there's little friction at the top where the wire is attached to the hook at the top. If a pendulum was swinging in a vacuum and the top hook was made with magnets that don't touch, then it would swing forever (at least a long time since you can't isolate the pendulum completely from the universe).


Greenhouse Gases and Pollution: Most of our energy comes from fossil fuels. The unfortunate consequences of this as you learned is that at a minimum it produces the two global warming (greenhouse) gases of water vapor and carbon dioxide. Since burning of fuels is done with air instead of just oxygen, we get nitrogen oxides forming. These are toxic and contribute to pollution. If the fossil fuels have impurities, such as sulfur, these impurities will end up in the air we breathe.

The energy in lightning splits oxygen molecules. These atoms of oxygen are very reactive and will immediately combine with other gases they encounter. If one bumps into nitrogen, it will form dinitrogen oxide. If it hits an oxygen molecule, it forms ozone. Both are toxic. Additionally, any sources of high voltage or electric sparks can do the same thing. Copy machines, laser printers, electric drills, spark plugs, bug zappers, vacuum cleaners, TV sets, and other similar devices can produce these toxic products. High energy can produce molecules of high energy, which are often dangerous.
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Last updated 2-8-09
Since Feb 18, 2008