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How fast is the world spinning in miles per hour? In this lesson students use unit rates to find the speed at which the Earth rotates around the Equator, Tropic of Cancer, and Arctic Circle. Think the Earth spins at the same speed everywhere? Think again!

### Students will

• Given the circumference of the Equator, find the speed of a point on the Equator
• Use the relationship between distance and time to reason about relative speeds
• Given the circumferences of the Tropic of Cancer and the Arctic Circle, calculate the speeds there
• Explain why the farther you travel away from the Equator, the more slowly you travel due to Earth's rotation

### Before you begin

This is an application of d = rt with long distances. Students should have already been introduced to the idea of unit rate as it relates to speed: a speed tells you a distance traveled within one unit of time.