Kathy Mashburn, age 9, of Stroud, Oklahoma, for her question:

 What makes the rivers move?

Water is a runny liquid. It cannot stand up by itself like, say, a log of wood or a bar of soap. Those substances are solid, stiff enough to stand up without being supported. Water must have a floor and walls in which to rust. Otherwise it flows along until it finds walls to support it. And when it flows, water always goes in a downward direction.

The streams and rivers are made of flowing water. They move along because new water is always pushing from behind. Sometimes the water finds a big deep hollow where it can rest awhile. It forms a lake. Otherwise the moving water flows down, down to the lowest part of the land. And the lowest land is at the seashore. So the flowing rivers are all weaving and winding their way down, down to loin the sea.