Question

An illustration of the earth with 5 horizontal lines labeled 60 N, 30 N, 0, 30 S and 60 S.
At which latitudes shown in the image of Earth do people experience the greatest tangential speed? Explain why.

Answer 1

The greatest tangential (linear) speed is at the equator (0°).

Reason: the Earth’s angular rotation rate ω is the same everywhere, but the linear speed v = ω r depends on the radius r of the circular path around the rotation axis. That radius = R cos(latitude), so
v = ω R cos(φ).
cos(φ) is largest at φ = 0°, so v is largest at the equator. (Latitudes with the same |φ| in N and S have the same speed.)

Examples (using R ≈ 6.37×10^6 m and one sidereal day):
- 0° (equator): ≈ 465 m/s ≈ 1670 km/h
- 30°N/S: cos30° ≈ 0.866 ⇒ ≈ 403 m/s ≈ 1450 km/h
- 60°N/S: cos60° = 0.5 ⇒ ≈ 232.5 m/s ≈ 837 km/h