Give Now

A Moment of Science

A Three Foot Orbit

Science tells you that you weigh less standing on the equator than you do at the north pole. Learn more on this Moment of Science.

Tracking and data relay satellite in hangar

Photo: cliff1066 (flickr)

Satellites like this one orbit the earth seventeen times faster than the earth rotates, balancing "fling" with gravity

Science tells you that you weigh less standing on the equator than you do at the north pole.

This is because the earth is rotating. At the poles you just turn around in one spot. On the equator, however, you are traveling in a giant circle. That means that you are constantly being flung outward, something like riding a very fast merry-go-round. Gravity keeps you from actually flying off the planet.

Now let’s try increasing the spin of the earth to add more fling. At 17 times its present spin, your weight at the equator would be zero. Fling has balanced gravity, and if you were to climb a three-foot ladder and step off, you would stay in midair, orbiting the earth at an altitude of three feet.

Okay, let’s have a little quiz to see if you’ve been listening. How many times per day does a satellite in low orbit go around the earth?

Sounds like an unrelated question? It isn’t. Those who guessed 17 are right on the money.

The situation with a low satellite is the same as our imaginary scenario where we sped up the rotation of the earth. All that is necessary to achieve orbit is to balance fling with gravity. You can do that in your imagination by speeding up the earth until it tosses us away from its surface. Or, you can send a satellite on a rocket around at the same rate of speed and the effect will be the same.

After all, from the satellite’s point of view, it’s the earth that’s suddenly rotating 17 times faster.

Stay Connected

What is RSS? RSS makes it possible to subscribe to a website's updates instead of visiting it by delivering new posts to your RSS reader automatically. Choose to receive some or all of the updates from A Moment of Science:

Support for Indiana Public Media Comes From

About A Moment of Science

Search A Moment of Science