Jeff Keith, age 13, of Cleveland, Ohio and Helen Rice, age 13, of Winner, S.Dak., for their question:

What actually causes thunder?

For countless ages, there was no sound in the world like a clap of thunder. Then mankind learned to fly  faster than scound and we get a man made clap of thunder every time a fast plane breaks the sound barrier. In both cases, the roar is caused by an explosion, a terrific explosion. A clap of thunder follows close on the heels of a lightning flash and occurs because the searing electricity hats a path of air in the moist cloud.

Warm air expands and the streak of hot air in a thunderhead must expand in a hurry, But the surrounding air of the moist cloud resists and holds it back and the expanding hot air explodes. It breaks its prison walls with a roaring clap of thunder.