The common misconception
Most people assume astronauts float because they are "far away" from Earth and gravity has stopped pulling them. It sounds logical. They are up in space, hundreds of kilometers above us, so maybe gravity just fades out up there.
But it does not.
The International Space Station orbits at about 408 km above Earth's surface. At that altitude, Earth's gravitational pull is still roughly 89% of what you feel right now sitting in your chair. The ISS and everyone inside it are being pulled toward Earth with enormous force every single second.
So if gravity is almost the same up there, why do they float?
The real answer: they are falling
Astronauts float because they are in free fall. Constantly. The ISS is not hovering in space. It is falling toward Earth at all times. But here is the key: it is also moving sideways so fast that it keeps missing the planet.
Picture this. Imagine you throw a ball horizontally from a very tall tower. It curves downward and hits the ground. Now throw it faster. It curves down but travels further before landing. Throw it fast enough and something strange happens: the ball keeps falling, but Earth's surface curves away beneath it at the same rate. The ball never lands. It just keeps falling around the Earth.
That is an orbit. And that is exactly what the ISS is doing.
An orbit is not floating. It is falling and missing the ground, forever. The astronauts, the station, and everything inside are all falling together at the same rate, so nothing pushes against anything else. That is why they feel weightless.
Physiworld's Gravity section covers exactly this concept with an interactive Anti-Gravity Room simulation where you can flip gravity and watch objects respond in real time.
How fast is "fast enough"?
For the ISS to stay in orbit, it needs to travel at roughly 28,000 km/h. At that speed, it completes one full orbit around Earth every 90 minutes. That means astronauts see about 16 sunrises and 16 sunsets every day.
If the ISS were to suddenly stop moving sideways, it would fall straight down to Earth, exactly like any other object. The only reason it stays up is its horizontal speed. There is no engine holding it up. There is no anti-gravity device. Just speed and geometry.
But wait, why does gravity get weaker with distance?
It does. And Newton figured out exactly how in 1687. Gravitational force drops with the square of the distance between two objects. Double the distance, the force drops to one quarter. Triple it, one ninth.
This is why gravity at the ISS altitude is 89%, not 100%. The station is further from Earth's center than you are, so the pull is slightly weaker. But "slightly weaker" is nowhere near zero.
The exact relationship between mass, distance, and gravitational force is described by a single equation. But rather than just reading it here, it is much more powerful to see how changing the numbers changes the force.
Physiworld breaks down F = GMm/r² with worked examples, interactive challenges where you plug in different masses and distances, and a Solar System simulation showing how gravity varies across planets.
Why does this matter?
Understanding that orbiting is falling changes how you think about everything in space. The Moon is falling toward Earth right now. Earth is falling toward the Sun. Even you, right now, are falling toward the center of the planet. The ground just happens to stop you.
Once this clicks, other things start making sense too. Why satellites do not need engines to stay up. Why the Moon does not crash into us. Why astronauts train in swimming pools (it simulates the feeling of everything falling at the same rate around you).
Gravity never turns off. Objects in orbit have simply learned how to fall with style.
Astronauts float because they are in constant free fall around Earth. Gravity is still pulling them. They are not floating despite gravity. They are floating because of it. The ISS moves sideways so fast that it keeps falling around the planet without ever hitting the surface.
Test your understanding
3 questions based on what you just read.
The Gravity section on Physiworld covers free fall, Newton's Law, orbital mechanics, and more through 5 interactive lessons with simulations, challenges, and XP rewards.