Course 4.2Lesson 1 of 3
Energy is the ability to do work, and it is measured in joules. It has many forms, and it changes from one form to another without being used up. Most of our energy comes from the Sun.
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Try the code and the simulations beside the lesson.
A hammer lying on the table does nothing to a nail. A hammer that moves fast drives the nail into the wood: it can do work. We say it has energy.
Energy is the ability to do work. The more energy an object has, the more work it can do. So energy is measured in the same unit as work, the joule (). A body that does of work gives away of energy.
| Form | Where we find it |
|---|---|
| Kinetic energy | A moving cart, a running child, the wind |
| Potential energy | A stone on a roof, a stretched rubber band, water in a high tank |
| Heat energy | A cup of hot tea, a fire |
| Light energy | The Sun, a lamp |
| Sound energy | A drum, a shout |
| Electrical energy | A current in a wire |
| Chemical energy | Food, fuel, a battery |
| Nuclear energy | The Sun, a nuclear power station |
In this course we study two of them with a formula: kinetic energy, the energy of motion, and potential energy, the energy of position or shape.
Energy is not used up. It changes from one form to another.
We can write each one as an energy chain, with arrows from one form to the next.
Energy Forms and Changes, a PhET simulation
The simulation is by PhET Interactive Simulations, University of Colorado Boulder (CC BY 4.0).
Most of our energy comes from the Sun. Plants use sunlight to make food, and we eat the food. Coal and oil come from plants and animals that lived long ago. The wind blows because the Sun heats the Earth unevenly, and rain falls because the Sun lifts water into the sky. A few sources do not come from the Sun: heat inside the Earth, the tides, and nuclear energy.
When work is done on an object, it gains energy. When an object does work, it loses energy. A girl who lifts a box does work on it, and the box gains energy. That is why work and energy share the joule.
Watch out. Do not say that energy is 'used up'. It changes form, often into heat that we cannot easily use again. That heat is lost to us, but it is not destroyed.
Write the energy chain of a hydroelectric power station, where water stored behind a dam turns a turbine.
So: potential, then kinetic, then electrical energy.
The program follows the energy along the chain of a torch.
Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.
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