To find Earth's equatorial rotation speed, we should divide the circumference of Earth by a 24 hours (1 day). To find the rotation speed at any other latitude, you need the following fact: The radial distance from Earth's axis at any latitude is equal to the equatorial radius times the cosine of the latitude. (Hint: When using the cosine (cos) function, be sure your calculator is set to recognize angles in degree mode, not in radian or gradient mode.) The radius of Earth is 6380 kilometers. Vi = 1370 km/hr Find the rotation speed for a person at latitude 35°N.