Yes there is gravity. In fact, on the International Space Station (ISS) which orbits Earth at an altitude of around 220 miles (354 km), the force of gravity is still about 90 percent to what it is here on Earth. So how can the ISS be in “zero gravity”?
Well, let’s start with the term “zero gravity.” It is unfortunate that this term gets used so much as it implies exactly that — zero gravity — which is misleading. The correct term is “microgravity.” This is the condition where people or objects “appear” to be weightless, for example, how astronauts and objects can “appear” to float in space.
Gravity can be found everywhere in space, the strength may vary, but it is always there. It causes objects to be pulled toward it; it’s also what holds the moon in orbit around Earth. Gravity is why Earth orbits the sun, and it also keeps the sun in place in the Milky Way galaxy.
A spacecraft could go far enough away from Earth that astronauts inside would feel very little gravity; however this is not why things float on the ISS. In fact it is this relatively strong gravity that holds the ISS in orbit, otherwise they would simply fly off into deep space.
How do astronauts float if 90 percent of Earth’s gravity reaches the space station? The simple answer is that they are in free fall; in the vacuum of space gravity that causes all objects to fall at the same rate (the mass of the object does not matter).
If you were to drop a rock and a feather at the same time on Earth, the feather would move slower because of the air around it. However, in a vacuum there is no air, therefore they would fall with the same acceleration.
An example would be if you were on a free-fall ride at an amusement park that had its own cabin, and you let go of an object at the same time as you begin to fall, you and the object would fall at the same acceleration.
When falling at the same acceleration, the object would appear to float in front of you; this is what is happening on the ISS. The crew, any objects, and the space station itself are all falling together around Earth giving the appearance that they are floating when you compare it with the spacecraft.
How does the ISS fall around Earth? Earth’s gravity constantly pulls objects downward toward its surface; this includes the ISS, so that means that it is constantly falling toward Earth’s surface. However, it is also moving at an extremely fast speed — 17,500 miles per hour (28,164 km per hour), a speed that matches the way Earth’s surface curves.
Imagine a baseball being thrown, gravity causes it to “curve” down hitting the ground quickly. When a spacecraft is orbiting Earth it travels at a speed so the curve of its fall matches the curve of Earth, this means that it is still falling toward the ground, however never hits it, the result, they fall around the planet. The moon stays in its orbit for this same reason, the moon is also falling around Earth.