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How fast is the planet spinning? In this lesson students use rates, arc length, and trigonometry to determine the speed at which points on the Equator, Tropic of Cancer, and Arctic Circle travel due to the Earth's rotation. Think the Earth spins at the same speed everywhere? Think again!

Students will

  • Given arc length and central angle, determine circumference of the Earth
  • Use the period of rotation (one rotation every 24 hours) to calculate the rotation speed in miles per hour
  • Given latitudes (central angles), determine circumference of latitude circle and speed of a point on that latitude, both for specific latitudes and generally
  • Explain why the farther you travel away from the Equator, the more slowly you travel due to Earth's rotation

Before you begin

This lesson is an application of d = rt, arc length, right triangle trigonometry, and the cosine function. If a class is unfamiliar with any of these ideas, the teacher will need to scaffold them.

Common Core Standards

Content Standards
Mathematical Practices

Additional Materials

  • Globe (optional)