June Dufty, age 10, of Millbrook, Ontario, Canada, for her question:

Why doesn't our air go off into space?

You know about gravity, that mighty force that hugs us close to the ground. It reaches up from the center of the solid globe and pulls at everything on the surface. If a stone falls from a high cliff, gravity drags it down in a hurry. If you throw a ball into the air, gravity gradually pulls it back to earth. If you lose your balance, gravity makes you fall to the ground.

This mighty force of gravity reaches up and outward on all sides of the globe. Since it is plain energy, tae cannot see it or smell it or hear it. But its strength works up through the air, pulling and hugging it close to the earth. The filmy air is allowed to blocs around. But our huge atmosphere cannot escape the pull of gravity and take off into space.