Gravitational energy is the movement of an object or mass that is caused by the pull of gravity. This is caused on Earth by the strong attraction of all other masses to be drawn back to Earth's center. An example of gravitational energy is water from a river tumbling over a cliff to form a waterfall.
When an object is lifted from the ground, energy is created and stored in the objects' gravitational field. The amount of energy stored is directly related to the distance between the object and the ground. The higher an object is lifted, the more the energy is stored in the gravitational field and the more energy that object produces as it returns to Earth.
Gravitational energy is often harnessed and used as a source of clean power for consumption. Hydro power is energy produced by the force of falling water, such as water in a reservoir behind a dam. When the dam is open and water is allowed to pass through to lower ground, the energy from the force created is accessible. The Hoover Dam in Arizona can produce more than 2,000 megawatts of capacity by utilizing gravitational energy. The average yearly generation of 4.5 billion kilowatt hours serve the electrical needs of approximately 8 million people in parts of Arizona, California and Nevada.