Spinning in Circles

We humans are traveling around in circles without even knowing it. We travel a circle around the axis of the earth once a day, and an almost-circle around the sun once a year. Considering each trip independently, how fast do we travel in each circle? (Assume we’re on the equator.) Here are some helpful data:

  • The diameter of the Earth is 12,756 km at the equator;
  • The distance from the Earth to the sun is 149,600,000 km;
  • There are 365.26 days in a year.
  • Give each answer in kilometers per hour.


    Show/Hide Solution

    The earth’s circumference is pi(12,756) km = 40,074 km in 24 hrs.

    40,074 km  = 1670 km/hr (slight rounding).
    24 hrs


    This is about 1040 miles/hr at the equator.

    In traveling around the sun, we go around a circle (roughly) of radius 149,600,000 km in 365.26 days.

    We travel 2pi(149,600,000) km = 939,964,522 km in 365.26 x 24 hours = 8766.24 hours.

    This divides out to 107,191 km/hr or 66,995 mi/hr, nearly 67,000 mi/hr hurtling through space.

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