Why astronauts float in space, even though gravity is still there
What is an orbit? Why the space station falls and never lands
People have lived on the space station for more than 25 years, and it is falling the whole time. So why does it never hit the ground? Isaac Newton found the answer with a cannon that only ever fired in his head.
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At a stall, Rono throws balls. Each ball flies forward and falls at the same time, so its path bends down to the ground. The harder he throws, the farther it lands.
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More than 300 years ago, Isaac Newton played the same game in his head. He put a cannon on a very high mountain, with no air in the way. More gunpowder, more speed, and the ball lands farther around the Earth.
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Here is the trick. In one second, any ball falls about 5 m. And the Earth is round, so the ground curves away under a ball that flies straight ahead. After 8 km, the ground is also about 5 m lower.
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Now fire the ball at 8 km every second. In each second, it falls 5 m, and the ground drops 5 m away under it. It falls all the time and never gets any closer. This fall that never ends is called an orbit.
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The station does exactly that. Up there the pull is a little weaker than at the ground, so a little less speed is enough: about 28,000 km/h, once around the Earth every 90 minutes. Every day, the crew sees 16 sunrises.
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Rono looks up. Behind the drop tower, the Moon comes up. It is almost 1,000 times farther away than the station. It does not fly away, it does not fall on us, and one lap around the Earth takes it almost a month.
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Quick check
Think of the 5 m that a ball falls every second.
Show the answer
Its path bends down faster than the ground curves away. It drops lower, into thicker air that slows it even more. In the end it falls, and most of it burns up on the way down.
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Go further
How the station got up there, and why it needs a push from time to time.