Zero Gravity

You have probably seen the astronauts floating around in the space shuttle. It looks like there is no gravity there and even the astronauts call it "zero gravity" or sometimes "micro gravity" meaning very little gravity.

This is hard to explain, but there is gravity everywhere in the universe! Without gravity everything would just fly apart - including the universe. Think of the moon. It is earth's gravity that holds in there and prevents if from flying off. Obviously the earth's gravity effects objects even as far away as the moon.

Of course the effect of earth's gravity grows weaker the farther away you are. On the space shuttle, however, you are really not that far away so the pull earth's gravity is about the same as on earth. This is hard to understand and even many adults cannot explain it correctly. I bet even your teacher thinks there is no gravity in space! Go ahead and ask - we'll wait.

So why then are the astronauts floating around? Basically, the shuttle is in a constant state of free fall - it is simply falling towards earth continuously. It's kind of like sky diving but in this case the shuttle is moving forward so fast it keeps missing the ground. The astronauts in the shuttle are also falling with the shuttle so it is like sky diving inside the shuttle - you fly around like you are weightless and this gives the illusion of zero gravity.

Being weightless, however, doesn't mean you are massless (or without mass). A 100 kilogram person's body still contains the same 100 kilograms of mass as on earth. If that person needed to move a 100 kilogram object they would not be able to unless they could anchor themselves to something much more massive - such as the space shuttle itself. To prove this to yourself, try throwing a really heavy object while on roller blades. Even with friction, you will roll backwards and the object will not go as far as if you were anchored to the ground - like not wearing roller blades.

Check out this explanation from the National Air and Space Museum - Is There Gravity In Orbit?

Click here for a more detailed explanation and a cool program that demonstrates weightlessness and orbiting.

How Things Fly is a great exhibit from the National Air and Space Museum.

Source: The Cosmic Perspective; The National Air and Space Museum