Why astronauts float in space, even though gravity is still there
Why the Moon does not fall on the Earth, and why higher orbits are slower
The Moon is almost 1,000 times farther away than the space station, and the Earth still holds on to it. So why does the Moon not fall on us? And why does one lap take almost a month, when the station takes 90 minutes?
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1
Newton wondered about this too. The pull that drops an apple from a tree: does it reach all the way to the Moon?
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2
It does. Count from the middle of the Earth, as before: the Moon is about 60 times farther from it than you are. Twice as far means a pull 4 times weaker, so 60 times as far means 60 × 60: about 3,600 times weaker. Weak, but never zero.
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3
Like Newton's cannonball, the Moon falls toward us all the time. Each second, it falls about 1.4 mm. In the same second, it moves about 1 km sideways, and that is just enough to miss the Earth.
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4
Far from the Earth, the pull is weaker, so it bends the path of the Moon less. The Moon does not need to go so fast to keep missing the Earth. The station races around in 90 minutes. The Moon, slower and on a far bigger circle, takes 27 days.
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5
Between the station and the Moon, other machines fall around the Earth too. GPS satellites fly about 20,000 km up. They are higher than the station, so they are slower: about 14,000 km/h. They are much lower than the Moon, so they are faster: twice around the Earth every day.
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6
On the way out, the bright dot crosses the sky again: the station has gone once more around the Earth. It is falling right now, with the crew, their pens and their food. It flies sideways so fast that it keeps missing the Earth. That is why they float.
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7
At the gate, Miva opens the map on her phone to find the car park. Her phone uses GPS satellites to put her dot on the map. But how, from 20,000 km away? Find out in "How GPS works: how your phone knows where you are".
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Quick check
Think of how long one lap takes, up there.
Show the answer
Higher, about 36,000 km up. Up there, one lap takes one day, as long as the Earth takes to turn once, so it stays above the same spot.
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Go further
The same fall works all the way out to the Sun.