Ask the Astronaut: What is free fall?

Astronauts Shane Kimbrough and Sandy Magnus play with floating food during the STS-126 shuttle mission.

Q: What is free fall?

Although free fall and weightlessness describe the same condition, free fall is the more accurate term. Free fall is the special type of motion that happens when the only force acting upon an object is gravity—there are no other forces such as friction, air resistance, tension, or anything pushing or pulling on the object.

 Newton’s second law of motion tells us that in free fall, all objects will fall with the same acceleration, regardless of their mass (which on Earth we refer to as “weight”). This is the situation in a spacecraft orbiting Earth: the spacecraft and its occupants and all the objects in the vehicle are actually falling around Earth. It’s as if you’re all in an elevator plunging down a shaft in a tall skyscraper. Inside the elevator, everyone and everything appears to “float,” because you’re all accelerating at the same rate. Fortunately, because the Earth is a near-sphere, astronauts in this special condition of orbital free fall never hit the bottom of the elevator shaft.

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