Gravity Is a Mystery (Let's-Read-and-Find-Out Science 2)

What goes up must come down.

Everybody knows that. But what is it that pulls everything from rocks to rockets toward the center of the earth? It's gravity. Nobody can say exactly what it is, but gravity is there, pulling on everything, all the time. With the help of an adventurous scientist and his fun-loving dog, you can read and find out about this mysterious force.