WHAT IS ENERGY?
By Roger Aiken

(CLICK HERE to learn more about Roger's work at the CREED website.) 

When I teach courses on Energy Issues, that is one of the first questions I ask my students. The answers I get range all the way from personal feelings of strength and vitality to the "stuff" that's found in oil or gas and heats our homes and runs our cars. Energy is an elusive concept, partly because we use it every day without giving much thought to what it is, partly because it means different things to different people and partly (or perhaps mostly) because in many of its forms it cannot be handled, seen or measured in the same way most material things like food, clothes, cars and boom boxes can. 

Yet because we use energy we enjoy a high standard of living; without it we would have no electricity, could not drive our cars, and we would have no computers, TVs or other manufactured goods. The whole of modern industry as we know it today would not exist. We would rapidly revert to the stone age. But even in the stone age people used energy in different forms, so we need to discover exactly what this elusive "stuff" is. If we start by looking up a dictionary we find there are many definitions of the term. The Random House Dictionary of the English Language has no fewer than nine definitions for energy. No wonder energy means different things to different people. 

Scientists, engineers and technologists, the people who make and run things, have a very precise definition for energy. It is "The capacity or ability to do work." That is, to get things done. But now we need to know what they mean by the word work. Technical people define work as "The product of a FORCE acting on a body and the DISTANCE the body moves in the direction of the force." The forces with which we are most familiar are those of gravity and friction and we all do work against these forces every day when we climb stairs or push things across the floor. And whenever we do these activities we use or expend energy. 

Energy is available to us in several different forms and has two distinct states or behaviors. Consequently we can classify energy in different ways. The two behaviors or states of energy are known as potential and kinetic. Potential energy is energy at rest or stored and waiting to be used. Examples of potential energy are:- 1. the energy stored in the water of a hydroelectric dam by virtue of its elevation. 2. the energy stored in chemical fuels such as coal, oil and natural gas. 3. the energy stored in the stretched material of an extended or compressed spring. Kinetic energy is energy associated with flow or motion. Examples of kinetic energy are:- 1. the energy of flow or movement of water in a river or in the turbine penstock at a hydroelectric power station. 2. the energy associated with the combustion of fuel in an engine. 3. the energy of current flow in an electrical circuit. 


"Scientists, engineers and technologists, the people who make and run things, have a very precise definition for energy. It is 'The capacity or ability to do work.'" 
The six forms of energy

Some of the forms energy can be classified into are:- 

1. Mechanical Energy. This is the form of energy associated with the position or movement of bulk matter and as such is probably the form with which we are most familiar and understand most easily. Examples already given are those of water in a hydroelectric dam or flowing down a river and of the stretched spring. You can also think of speeding cars, spinning tops or flywheels and compressed air in a pressure tank. 

 
Technical people define work as "The product of a FORCE acting on a body and the DISTANCE the body moves in the direction of the force." 

2. Electrical Energy. This is also familiar to us since we use it to run our appliances computers and TVs to light our buildings power electric motors. It is the energy associated with the storage and flow of tiny particles called electrons in electric circuits and also in natural events like lightning. 

3. Thermal Energy. Thermal energy is also known as heat. It is contained within material as a result of the vibration of their molecules. The intensity or level of this vibration is measured by the material's temperature. We need thermal energy to heat our homes in winter and conversely when it is hot in summer we remove thermal energy (heat) from our buildings with air conditioners. 

4. Chemical Energy. This is the energy associated with the attraction between atoms in fuels and other materials. Individual atoms are connected to each other by linkages known as chemical bonds and when these are broken or rearranged in a chemical reaction, energy is either absorbed or given up usually in the form of heat. In the case of chemical fuels the reaction is known as combustion and energy is given up as heat. 

5. Nuclear Energy. This is the energy associated with the binding together of protons and neutrons in the nuclei of atoms. These "binding forces" are extremely strong and so if they are broken as in a nuclear bomb or in a controlled way in a nuclear reactor, enormous amounts of energy are released. The processes by which some of this binding energy are released are known as nuclear fission, nuclear fusion and radioactive decay. Radioactive decay is always present along with fission and it is because some of the decay products are so toxic and dangerous that people have always been so concerned about nuclear power. 

6. Radiant Energy. This is an electromagnetic phenomenon and perhaps the most difficult energy form to understand. Yet this is the form in which we receive energy from the sun and most of the warmth from a blazing fire. To describe this form of energy fully one has to think about it both as a wave motion and a flow of particles. What makes it more difficult to understand is that radiant energy comes to us from the sun through empty space!! But without the radiant energy we receive from the sun, earth would be a cold dead place where nothing could live. 

In order to use energy it is necessary to convert it between its different forms so that it can be moved from sources to end-users and supplied in the form most useful or amenable to the task it is required to do. Some of these interrelationships and conversion processes are shown in a linked diagram--CLICK HERE to see the diagram.

Learn more about Roger Aiken's

Center for Global Environmental Education
Hamline University Graduate School of Education
1536 Hewitt Avenue, St. Paul, MN 55104-1284
Phone: 651-523-2480 Fax: 651-523-2987
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