Why Astronauts Float Even Though Earth Gravity Is Still Strong
At about 400 km up, Earth gravity is still nearly 90% as strong as on the surface, but astronauts float because they are in continuous free fall.
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Astronauts do not float in orbit because they have escaped Earth gravity. At the height of the International Space Station, roughly 400 kilometers above Earth, gravity is still close to 90% of its strength at the surface. NASA describes the floating sensation as microgravity because the station and everything inside it are continuously falling together. The station is also moving sideways extremely fast, so its path curves around Earth instead of sending it straight down to the ground. The result is a constant state of free fall in which astronauts, spacecraft, and loose objects share nearly the same acceleration, so there is very little contact force pushing an astronaut against a floor. That is why the experience feels weightless even though Earth gravity remains the main force keeping the station in orbit. Small effects such as atmospheric drag and tiny differences in gravitational pull across the station still exist, which is why the environment is called microgravity rather than absolute zero gravity.
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