Is there gravity in space? An answer of “no” makes sense as astronauts on the International Space Station (ISS) float around within the spacecraft. At the same time, an answer of “yes” makes sense as this spaceship does orbit the Earth? What is the right way to think on this problem?
To begin with, yes, there is gravity in space. The gravity we feel is caused by the attraction that all of us feel towards the center of the Earth.
The relevant bit is that the gravitational force depends on the distance between the center of you and the center of the Earth. As the distance between you and the Earth increases, the gravitational force decreases. Here are some examples.
If we go to the highest floor of a skyscraper, then do we feel lighter than when we are on the ground? Yes, technically we do, but the difference is too small to mention. How about the top of a mountain? Yes, there is less gravity there too, and the difference is also very small. Now then, what if we go to the ISS?
The ISS orbits the Earth in space. It is very far from the center of the Earth compared to the skyscraper. And this time the difference results in a measurable difference. On the ISS we feel a downward pull of gravity that is 88 percent of that on Earth.
This leads us to the interesting part: if we would feel a not-so-different pull of gravity in space, then why do astronauts float? They should be standing up normally, but feel just a bit lighter, right? Well, not quite.
It is the fact that the spacecraft plus astronauts are constantly in free fall that makes them feel weightless. We can get at this idea with another example. When one jumps off of the high dive at the local swimming pool, recall that a nauseous feeling, almost like the stomach wants to fly up into the heart. This is because during that short-lived journey towards the surface of the water we are in free fall. This makes us feel weightless (and for many of us that is a most uncomfortable sensation).
Likewise, in space we are constantly falling towards the Earth. In other words, in space also feel like we are falling down off the diving board towards the water, but in this case the duration of that scary “fall” never ends. Orbiting around Earth is really just another way of saying that we are constantly falling towards Earth but just manage to miss it, over and over again.
