Condition for Free Fall around Earth
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For a body to stay in orbit around Earth, it must travel tangentially (magenta arrow) with a velocity that lets the body fall a radial distance due to the force of gravity (black arrow) in such a way that it follows the curvature of Earth (yellow arrow). The resultant displacement can be represented as the sum of both motions (blue arrow). As an example, astronauts inside a space shuttle appear to be floating in zero gravity with an absence of gravity, but actually they are continuously falling around Earth.[more]
It is easy to calculate that near Earth's surface a body must travel tangentially at about 7.9 kilometers per second to stay in orbit.[less]
Contributed by: Enrique Zeleny (March 2011)
Open content licensed under CC BY-NC-SA
"Condition for Free Fall around Earth"
Wolfram Demonstrations Project
Published: March 7 2011