Here are some of the basic things about energy that you need to know. Knowing these things will help you understand what energy is and how to use it wisely.
Useful Definitions:
To walk the energy walk, you have to talk the energy talk. These definitions will help you converse intelligently about energy:
Kinetic energy: energy of motion, such as moving objects, vibrating molecules, light and sound waves.
Potential energy: stored energy, such as water behind a dam, coiled springs, energy in molecular bonds.
Mechanical energy: just another name for kinetic and potential energy.
Renewable energy: energy that can be replenished in a short amount of time. Energy from the sun and biomass, chemical energy stored in plants and animals are examples.
Nonrenewable energy: energy sources that have a fixed amount of supply on the earth, because they take a long time to form. Oil and natural gas are examples.
Fuel: something consumed to make energy.
Fossil fuels: fuels formed from the remains of prehistoric plants and animals – in other words fossils. Examples include coal, oil and natural gas.
Force: an influence that causes an object to speed up or slow down (i.e. accelerate or decelerate). It is also known as a push or a pull. There are four forces in the universe: gravitational, electromagnetic, the strong nuclear force (important in fusion reactions and holding the nucleus of an atom together), and the weak nuclear force (important in fission reactions).
Power: work done in a specific amount of time. An equal amount of work done more quickly takes more power. Thus a car accelerating more quickly is said to have more power.
Energy Efficiency: a measure of the useful energy to the total energy used to do useful work. Usually expressed as a percentage, it is calculated by dividing the useful energy gotten out of a system (moving a car) by the total energy used (gasoline used to make the car move) and multiplying by 100 (to get it in percent).
High Quality Energy: energy that is easy to capture and utilize.
Energy Conservation: behaviors that result in the use of less energy. Cycling instead of taking a car is an example.
Energy Efficient Technology: Technology that uses less energy to do the same amount work. A car that gets better fuel mileage is an example.
Energy Carrier: Something that contains energy that can be directly converted to useful work or heat. Examples include electricity, gasoline, hydrogen, batteries and springs, to name a few. It is the energy we commonly use in our daily lives.
Forms of Energy/How Energy is Measured
Energy comes in many forms. Work is done when one form of energy is converted into another.
Mechanical Energy
Kinetic Energy
Potential Energy
Electrical Energy – associated with the movement of electrons
Radiant Energy – electromagnetic energy that has wave and particle properties. Light is an example.
Thermal Energy – heat energy caused by the vibration, rotation, and movement of atoms and molecules
Motion Energy – the movement of objects from one place to another
Sound Energy – when molecules are vibrated, causing them to move in wave patterns
Chemical Energy – energy stored in the bonds of molecules. Biomass, oil and natural gas are examples.
Stored Mechanical Energy – energy stored in objects by the application of a force. Examples are compressed springs and stretched rubber bands.
Nuclear Energy – energy that holds the nucleus of an atom together. The energy comes from mass when atoms are split apart (fission) or fused together (fusion).
Gravitational Energy – the energy of position or place in a gravitational field. Examples are water behind a dam or a ball on top of a hill.
One of the things that can make energy confusing is the wide variety of ways we measure energy. We measure heat energy in units different than mechanical energy and different from electrical energy.
The energy content of fuels is measured in terms of the heat it can generate.
Btu or British Thermal Unit is the amount of energy required to raise the heat in one pound of water 1 degree Fahrenheit. A Therm is 100,000 Btu. A Quad is a quadrillion (1015) Btu.
A calorie is the amount of heat needed to raise one gram of water 1 degree Celsius. Food calories actually refer to kilocalories, or 1,000 calories.
Other energy measurements include the joule and the kilowatt-hour. It is easy to convert from one energy measure to another:
One Btu is equal to 252 calories or 1055 joules.
A kilowatt-hour is equal to 3,412 Btu.
One kilowatt-hour can light a 100 watt light bulb for 10 hours.
For a better feel for the energy content of common items, and the energy expended by typical activities, refer to the two tables below.
Energy Content/Utilization
Btu
A match
1
An apple
400
Making a cup of coffee
500
Stick of dynamite
2,000
Loaf of bread
5,100
Pound of wood
6,000
Running TV for 100 hours
28,000
Gallon of gasoline
125,000
20 days of cooking on gas stove
1,000,000
Food for one person for one year
3,500,000
Apollo 17's trip to the moon
5,600,000,000
Hiroshima atomic bomb
80,000,000,000
1,000 transatlantic jet flights
250,000,000,000
United transatlantic jet flights
250,000,000,000
United States in 2006
100,000,000,000,000,000
Adapted from the Materials Science and Technology
Teacher’s Workshop,
University
of
Illinois,
Champaign/Urbana
Energy Content of Common Fuels
(Adapted from the Dept of Energy)
1 barrel (42
gallons) of crude oil = 5,800,000 Btu
You need to know the rules of energy to understand how energy is made and transferred from one type to another. It also helps us to understand concepts like energy efficiency and why your battery runs down. The rules of energy are known as the laws of thermodynamics, which deal with energy and work. They were born out of studies of steam engines in the 19th century, but work for all forms of energy, not just heat. These laws help us understand and predict the operation and efficiency of machines.
Rule 1: Energy input equals energy output. Though energy can change forms, it does not increase or decrease. This is known as the law of conservation of energy. This means the total energy and mass of a system remains constant. Since mass does not change in most energy transformations (nuclear energy being the exception), the total energy of the system will remain constant.
Rule 2: You cannot achieve 100% energy efficiency. Though energy is conserved, some energy always goes into energy that is not useful. This is also known as the law of entropy, with entropy being a measure of the unavailability of a system’s energy to do work (often thought of as randomness, but better seen as the evening out of energy – hot items cool to room temperature). Entropy is why a dropped ball comes to rest on the floor. The rule also means that energy flows from high to low – a ball will not roll uphill; heat will not flow from cold to hot - energy inputs are needed to change this direction. Entropy will smooth out energy differences – heat, pressure, density, and other parameters will tend to equalize. With no energy differences, you can’t get useful work out - this energy is termed “useless”, and the more energy transformations you do, the more energy you lose, and the less efficient the system is. Perpetual motion machines are not possible!
Rule Zero: There is a lowest energy state, which is a temperature of absolute zero. It is -273.15 degrees Celsius. Molecular motion would stop at this temperature. Combined with the second rule, this means that everything, including our universe, will tend toward absolute zero, where no useful work will be possible. The temperature of empty space in our universe is about -270.5 degrees Celsius, just above absolute zero – not much useful work can be gotten from empty space! Fortunately there is not just empty space in the universe.
Kinetic energy: energy of motion, such as moving objects, vibrating molecules, light and sound waves.
Potential energy: stored energy, such as water behind a dam, coiled springs, energy in molecular bonds.
Force: an influence that causes an object to speed up or slow down (i.e. accelerate or decelerate). It is also known as a push or a pull. There are four forces in the universe: gravitational, electromagnetic, the strong nuclear force (important in fusion reactions and holding the nucleus of an atom together), and the weak nuclear force (important in fission reactions). 
