Figure 5.9: Hydroelectric dams like this one use the power of moving water to create elec-
tricity. ( 8 )
Water Power
Earlier in this lesson, you learned that energy can travel in the form of light and heat, just
as it does when it travels from the sun to the Earth. Now, you will learn about one way in
which energy can travel in the form of a moving object. In this case, the moving object is
water (Figure5.9). Water power uses the energy of water in motion to make electricity. It
is the most widely used form of renewable energy in the world, and it provides almost one
fifth of the world’s electricity.
In most power plants that use water power, a dam holds water back from where it would
normally flow. Instead, the water is allowed to flow into a large turbine. Because the water
is moving, it has energy of motion, called kinetic energy. The energy of this moving water
makes the turbine spin. The turbine is connected to a generator, which makes electricity.
Many of the streams in the United States where water flows down a slope have probably been
developed for hydroelectric power. This is a major source of California’s electricity, about
14.5 percent of the total. Most of California’s nearly 400 hydropower plants are located in
the eastern mountain ranges where large streams descend down a steep grade.
One big benefit of water power is that it does not burn a fuel. This benefit gives water power
an advantage over most other energy resources in how it affects the environment. Because
water power does not burn a fuel, it causes less pollution than many other kinds of energy.
Another benefit of water power is that, like the other resources you are learning about in
this lesson, it is a renewable resource. We use energy from the water’s movement, but we
are not using up the water itself. Water keeps flowing into our rivers and lakes, so wherever