Philosophy of Physics: A Very Short Introduction (Very Short Introductions)

by David Wallace

Why is it a zero-gravity environment? Far too often one hears that it’s because there is no gravity in space (presumably because it’s far away from the Earth’s gravitational pull). This is nonsense. The Earth has a radius of about 6,400 kilometres; the International Space Station orbits about 500 kilometres up; the gravitational pull of the Earth at 6,900 kilometres distance is scarcely less than at 6,400 kilometres. A better way to understand why astronauts don’t experience gravity is that everything in an orbiting spacecraft is moving freely under gravity, at the same rate: the astronauts, their possessions, and the walls of the spacecraft itself. So gravity does indeed pull the astronaut towards the wall of the spacecraft, but it also pulls the wall of the spacecraft away from the astronaut, and to exactly the same degree. Hence the better name for ‘zero gravity’: free fall.

interesting fact about zero-gravity