Nothing happens without energy. When you sit in the classroom, you need light energy. The computer or tablet you are using to read this book needs electric energy to work. Heat energy is needed to keep the classroom warm. You have arrived in the classroom by using kinetic energy. All the things you see around you are produced by using different kinds of energy. 

Energy sources can be either renewable or non-renewable. Renewable energy sources include water, wind, sunlight, and wood. They are share one common quality: the energy that is consumed when these energy sources are used will replenish. For example, new trees will grow as old trees are cut down and the sun radiates solar energy constantly. 

Non-renewable energy sources include nuclear power and fossil fuels such as oil, coal, and natural gas. These energy sources are diminished as they are used. In addition to the limited supplies of these resources, non-renewable energy sources are also linked to significant environmental problems.

The picture contrasts different forms of non-renewable energy sources (on the left) with renewable energy sources (on the right). What kinds of energy sources can you identify from the picture?