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# Rotation Symmetry

## When a figure can be rotated less than 360 degrees and look the same as it did before.

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This End Up

Objects with rotational symmetry don’t really have an “up” and a “down.” Instead, they remain the same even after you turn them. Rotational symmetry is essential for many machines. Without rotational symmetry, motors would freeze, wheels would stop turning, and the world would come to a halt.

#### From Grist Mills to Nuclear Power

People have taken advantage of rotational symmetry for thousands of years. Modern wind farms use the wind’s motion to turn their symmetric turbines. Power plants generate electricity by using parts that have rotational symmetry. Nuclear power plants use uranium, an element that can undergo decay, to generate heat. When the atoms in uranium split, they release heat energy. The power plants then use this heat to make steam, which turns turbines, generating electricity.

Hydroelectric plants like the one above also use rotating turbines to generate electricity. However, instead of relying on heat or steam to turn their turbines, they harness the movement of water to do the work. The power plant workers can control the flow of water through a hydroelectric dam in order to generate more or less power, depending on need. Rotational symmetry allows power plants to operate smoothly and to produce great quantities of power.

#### Explore More

Watch the videos below for more examples of rotational symmetry being put to good use.

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