When we see astronauts aboard the International Space Station, one of the first things we notice is that they seem to float.

Astronauts glide through the station. Food can drift away from them. Even objects that would be extremely heavy on Earth can be moved with very little effort.

It certainly looks like there is no gravity.

But here's the surprising part:

There is plenty of gravity in space.

In fact, gravity is the reason astronauts can orbit Earth in the first place.

So Why Do Astronauts Float?

Astronauts appear to float because they, their spacecraft, and everything inside it are falling around Earth together.

This condition is called microgravity.

Imagine dropping a ball. Gravity pulls it toward the ground.

Now imagine throwing that ball forward incredibly fast. As gravity pulls the ball downwardDid , the curved surface of Earth is also falling away beneath it.

If the ball could travel fast enough—and there were no atmosphere or obstacles in the way—it could continue falling around Earth without ever reaching the ground.

That's essentially what happens to an orbiting spacecraft.

The spacecraft is constantly falling toward Earth, but it is also moving forward so quickly that its path follows the curve of our planet.

The result is an orbit.

How Fast Is the Space Station Moving?

Very fast!

NASA explains that the International Space Station travels at approximately 17,500 miles per hour (28,000 kilometers per hour) as it orbits Earth.

At that speed, the station keeps falling around Earth rather than falling straight down toward the surface.

Everything inside the station is falling at the same time—the astronauts, their equipment, their food, and even tiny drops of water.

Because everything is falling together, the astronauts appear to float relative to the spacecraft around them.

Is There Really Gravity Up There?

Absolutely.

This is one of the most interesting parts of the story.

The International Space Station orbits only a few hundred miles above Earth. At roughly that altitude, Earth's gravity is still about 90% as strong as it is at Earth's surface.

So astronauts aren't floating because they've escaped Earth's gravity.

They're floating because of what gravity is doing to them.

Gravity is continuously pulling both the spacecraft and the astronauts toward Earth.

What Is Microgravity?

You may have heard people use the term zero gravity.

NASA explains that this description can be misleading. The more accurate term for the environment experienced aboard an orbiting spacecraft is microgravity.

Astronauts feel weightless because they and their spacecraft are in continuous free fall together.

Interestingly, you may have experienced something a little similar yourself.

That brief feeling of your stomach rising when a roller coaster suddenly drops over a hill is caused by a short period of free fall.

NASA can even create short periods of microgravity here on Earth by flying specially designed aircraft through large parabolic arcs. During part of the maneuver, the aircraft and everything inside it experience free fall together.

Why Does NASA Study Microgravity?

Microgravity isn't just fun for astronauts floating around the space station. It gives scientists an unusual laboratory for studying things that behave differently when the familiar effects of gravity are greatly reduced.

NASA uses microgravity research to study subjects ranging from the human body to materials and other physical processes. Understanding how people respond to long periods in microgravity is also important for future long-duration space missions.

Did You Know?

The next time you see an astronaut floating aboard the International Space Station, remember:

They're not floating because there is no gravity.

They're actually falling around Earth—at thousands of miles per hour!

Sometimes understanding why something happens makes it even more amazing.

Keep exploring. There's always something new to discover.