5.2 Energy
Our body cannot move unless we have energy from food. A car would not run without the energy it obtains from burning fuel. Machines in factories cannot run without consuming energy supplied by electricity. Any change in motion requires energy.
When we say that a certain body has energy, we mean that it has the ability of doing work.
lightbulbEnergy can be defined as the ability of a body to do work.
When someone does work, energy of the body has to be spent. In fact, energy is transferred to the body on which work is done. In other words, energy is transferred from one system to another. For example, when you do work pushing a swing, chemical energy in your body is transferred to the swing and appears as energy of the motion of the swing.
Like work, energy is a scalar quantity. Its SI unit is the joule (J).
When one joule of work is done on a body, the amount of energy spent is one joule.
There are many forms of energy. Electrical energy, chemical energy, nuclear energy, heat energy, and light energy are some well-known forms. There are two basic forms of energy:
- Kinetic energy
- Potential energy
The combination of these two types of energies is called mechanical energy.