Randy Hoey, age 11, of east St. Louis, Mo., for his question:

What keeps the earth from falling?

Nothing at all keeps our lovely old world from falling, falling at high speed through the heavens. In fact, it falls day and night at the fantastic speed of 18 miles a second. This is the average speed of the earth as it travels its orbit around the sun.

The gravity of the sun pulls our solid globe day and night with a mighty force. But the earth refuses to fall straight down into the sun. It overcomes the sun's gravity by swinging fast around and around its orbit. This changes the falling down direction into a falling around direction. As We travel at 18 miles a second on our 600 million mile orbit, We are really falling around and around the sun.