1. Energy.

Foods labels provide us information about the nutritional qualities of the food we eat. For example, the labels on the margin inform us about nutriotional qualities of the milk they go with. Thanks to this data, we can know the energy we'll get if we consume it.

In prehistoric times, muscular energy was the only source of energy that people had. Then different mechanism and machines were invented to make everyday tasks easier and improve people's quality of life.

1.1.Forms of energy.


1.2. Units of measurement for energy.
In the international System (IS), energy is measured in joules (J). When energy takes the form of heat, we often express it as calories (cal).
The relationship between calories and joules is: 1cal = 4.18J.

1.3. Power.
Power (P) is a measurement of how quickly work is done.
The power of a machine is the amount of work that it can do in a certain amount of time. We express this relationships as: P = W/t.
In the previous equation, P is power, expressed in Watts (W); W is work, expressed in joules; and t is time, expressed in seconds (s).

Energy conversion efficiency (%) = output/input · 100