Did you ever wonder how we could sit and walk-in the earth? The answer to that question is because there is gravity on earth. But space, on the other hand, doesn't have any air or even gravity. That is why the astronauts always float around in space. They can't walk properly. And there are some other fun activities you could try at home. You could get anything. For example, I have a pen. And when I let go of the pen the pen falls to the ground. What happened to your thing? Did it roll-off? Did it make a sound? Whatever it happened the whole point was it fell down. 

A long time ago the first person who found gravity was Newton. Sir Isaac Newton was an English mathematician and mathematician and physicist who lived from 1642-1727. The legend is that Newton discovered Gravity when he saw a falling apple while thinking about the forces of nature. Plus, if you're more interested in gravity you could look at the fun fact about gravity.

Earth's gravity comes from all its mass. All its mass makes a combined gravitational pull on all the mass in your body. ... You exert the same gravitational force on Earth than it does on you. But because Earth is so much more massive than you, your force doesn't really have an effect on our planet.