Measuring Energy

Energy is measured in Joules. Once upon a time energy was measured in calories, but this unit is now only used by people who are on a diet. You should be using Joules. One Joule is a very tiny amount of energy, you are much more likely to use KiloJoules or MegaJoules.

1Kj  =  1000j

1Mj  =  1000Kj  =  1000000j

You should know that there are several different forms of energy:

  1. Heat
  2. Light ~ including radio waves etc.
  3. Chemical
  4. Kinetic
  5. Potential
  6. Electric
  7. Sound
  8. Nuclear

Please don’t get confused about other kinds of energy. E.g. Fossil fuels contain energy: this is a form of chemical energy. When we burn fossil fuels the chemical energy is turned into heat energy with some light energy and even sound energy. You can use your common sense about this with many exam questions. Solar energy is a form of light energy: it is light from the sun.

The energy put into your car engine is chemical energy(petrol or diesel). When the engine is running, the chemical energy in the petrol (or diesel) is converted into kinetic energy (movement), heat energy and sound energy. As I said you can use your common sense. You should be able to see the movement of the engine if you lift the bonnet (you will see the fan moving); you will be able to hear the engine running; you will also be able to feel heat from the engine.

If a car engine was 100% perfect all the chemical energy from the petrol would be turned into kinetic energy. There would be no wasted heat or sound. When you are driving a car, some of the kinetic energy is converted into electrical energy by the alternator. This electrical energy is converted into chemical energy as the battery gets charged up. Electrical energy can be converted back into kinetic energy in electric motors: this happens with the windscreen wipers and the starter motor. Electrical energy is converted into light energy in the headlights. In fact the only kind of energy which you will not find in your car is nuclear energy.

If you are stuck in the exam, just think about your car!!!

So I did not mention potential energy. Well when you drive your car up hill, some of the kinetic energy is converted into potential energy. The higher up you go the more potential energy you have. It is not very safe to drive downhill with the engine off, but it is possible. Gravity pulls you down the hill. As you go downhill, potential energy is converted back into kinetic energy.

There is an important rule about energy: it cannot just disappear or come from nowhere.

Summary to be added.

Here are some suggestions for your revision index cards: write the words in red on one side of the card and the words in blue on the other side.

Forms of Energy: heat, light, chemical, kinetic, potential, electric, sound, and nuclear.

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