The ABC of Energy: The Definition of Energy

Part Two of a Gaia Discovery Energy Series based on "The Energy Trail – Where Is It Leading" by George H Croy, available at Amazon & other good book stores. 

From the previous column on the ABC of Energy what we learned so far was that the Sun is not Energy, but a ‘machine’ that converts energy from one form to another. So how can we define ‘Energy’ in an understandable form? The simplest way to describe energy would be to imagine it as a ‘means to do work’. In other words, by expending energy, we are able to do things.

Let’s consider a torch battery. Is it ‘Energy’? No. It is a metal case filled with chemicals. Those chemicals have abilities inherent within them to produce an electrical current, under specific circumstances. Flick the switch on the torch, and you get light. Ah! Is this energy? No. It is light, part of the electromagnetic spectrum mentioned previously. What has happened is that by closing the circuit on the torch battery, the chemicals release electrons that heat up the coil in the bulb until it glows, giving off light. It also gives off heat! You are converting one form of energy to another.

‘Energy’ can be defined in certain measurable forms, of which there are many. However, they are all derived from a few basic forms that can be used to describe the way energy appears to us. The battery is one form, and falls into the category of ‘Chemical’ energy. ‘Potential’ energy is another form, whereby work is available to be done by virtue of position. Think in terms of a reservoir behind a dam. The water, by virtue of its height, has ‘potential’ energy, or the ability to do work (drive a turbine) as it goes from a higher to a lower level.

‘Heat’ energy is one which most people will be familiar with. However, don’t confuse ‘heat’ with ‘temperature’. Temperature is just a measurement. Heat is the ability to do work. This is something that has to be understood – having ‘Energy’ is the ability to do work. If it doesn’t do work, then it can’t be classified as an energy source*. To raise the temperature of something, you have to add heat to it. To lower the temperature you would therefore have to remove heat.

Most people will also be familiar with ‘nuclear’ energy although few will fully understand how it is used in our day to day lives. If we go back to the previous column, we talked about the Universe, of protons and neutrons, electrons and such like. They are the principal building blocks of matter, of the atoms from which everything is made. In most energy conversion events, they play little or no part in the event (except electrons, as electricity) but in nuclear energy they play a very large part – as we will see in a later column.

Another form of energy is ‘Kinetic’ energy, that which is inherent in a body in movement, such as a hammer descending on a nail head for instance. You raised the hammer to a certain height using your muscles (energy input from the food that you eat) turned into kinetic energy as the hammer descends. What happens to the energy after that? Well, we begin with the sound of the hammer contacting the nail head. Then there is the heat generated at the nail head, as well as that caused by the friction of driving in the nail. Can you think of any other energy conversion? What drives the hammer as it rebounds? Every event can be broken down into one form or another of energy conversion.

Think about the energy that drives your car. What transformation takes place in running a car engine? You can find out in my book (see below) or you can wait until the next column.

 Next: Energy sources

*This is not strictly true as we will find out in a later column.

Read the other articles in this series:

Part One - The ABC of Energy: What is Energy

Part Two - The ABC of Energy: The Definition of Energy

Part Three - The ABC of Energy: Energy Sources

Part Four - The ABC of Energy: Applications & Consumption

Part Five - The ABC of Energy: Clean or Dirty Sources?