Why do astronauts float? (It is not because gravity is gone)
The most common misconception in spaceflight, explained simply — and the one-line sum that shows gravity is still almost as strong up there.
5 min read
Ask most adults why astronauts float and you will hear “there is no gravity in space”. It is the answer in a lot of children’s books, and it is wrong. Worse, it is the kind of wrong that makes the real explanation harder to learn later.
Here is the actual reason: they are falling. So is the space station around them. Because everything is falling together, nothing presses against anything else — and that feeling of not pressing on your seat is exactly what we call floating.
How much gravity is there really?
Gravity gets weaker with distance, but slowly. The strength at a height h above the ground is g₀ × (R ÷ (R + h))², where R is Earth’s radius of 6,371 km and g₀ is 9.81 m/s².
The International Space Station orbits at about 420 km. Put that in and you get roughly 8.6 m/s² — about 88% of the gravity you feel standing in your kitchen. Nothing has been switched off. An astronaut in orbit weighs almost what they weigh at home.
The lift analogy children actually get
If you have ever been in a fast lift that starts going down, you know the lurch in your stomach. For that half-second you weigh a little less, because the floor dropped away slightly faster than you did.
Now imagine the cable snapping — and please imagine it, do not test it. You and the lift fall at exactly the same rate. Your feet stop pressing on the floor. You float, in the middle of a falling box, with the full strength of Earth’s gravity acting on you the whole time.
That is the space station. The only difference is that the station is also travelling sideways at 27,600 km per hour, so instead of hitting the ground it keeps missing it. It has been falling since November 2000 and has not landed yet.
Why the sideways part matters
This is the bit that turns a misconception into real understanding. Going up is not what gets you into orbit. Going sideways fast enough is.
Newton worked this out with a thought experiment about a cannon on an impossibly tall mountain. Fire the ball gently and it lands nearby. Fire it harder and it lands further away. Fire it hard enough and the ground curves away beneath it as fast as it falls — so it never lands at all.
That is an orbit. It is not floating in a void; it is a permanent, very fast miss.
What to say to a seven-year-old
- “They are falling, and their spaceship is falling with them.”
- “Gravity is still there. It is nearly as strong as it is here.”
- “They go so fast sideways that they keep missing the Earth.”
Three sentences, all true, and none of them will have to be unlearned in secondary school.
Common questions
Is there gravity in space?
Yes. At the International Space Station’s altitude of about 420 km, gravity is roughly 8.6 m/s² — about 88% as strong as at the surface. Astronauts float because they are in free fall, not because gravity is absent.
Why do astronauts float if there is gravity?
They are falling, and their spacecraft is falling with them at the same rate, so nothing presses against anything. Because they are also moving sideways very fast, they keep missing the Earth instead of hitting it.
What is the correct name for floating in space?
Free fall, or microgravity. “Zero gravity” is a misleading term because gravity is still nearly as strong there as it is on the ground.