Paula Stieber, age 12, of Fairfield, Connecticut, for her question:

What causes a tornado to stop?

Everybody wants to know what causes a tornado to start and even the experts can¬not explain all the details. But what causes the raging twister to stop is a rare and interesting question. And it happens to be somewhat easier to answer. A storm, especially a wild little tornado, is a bundle of energy. And energy comes in a quota, so much and no more. It can be put to work or changed into some other kind of energy as steam energy is transformed into work energy to run an engine. And a quota of energy can use up its strength, as the sound energy of a drum fades while forcing its way through the air.

The tornado is a funnel of whirling winds sucked inward and upward by a central vacuum. When it strikes the ground, its energy is used to bash down buildings and tear up trees. This works off its energy and its original quota becomes less. The wild extravagance weakens it and after cutting a narrow path of destruction for a mile or so, the fierce winds subside to gentle breezes. The breathless tornado has to stop.