Salman Khan of Khan Academy explains something that I never really thought of before. Astronauts on the International Space Station appear to be free-floating, as they do somersaults around the station and sit on the ceiling and such. But the ISS is not that high above us, only 350 kms (200 miles) above our heads. So the gravity of the massive Earth should still be a major influence there. Yet they all look like they’re living gravity-free? So what gives?
Turns out that Earth’s gravity still has a large influence on the station itself and all it’s occupants. Gravity is what keeps it in orbit. In fact, the station is in constant free-fall. Gravity is pulling the station towards Earth but the station is moving so fast, that never actually hits the Earth.
That’s a scary thought. The only difference between a stable orbit and crashing to the Earth is the station’s kilometers-per-hour.