Patricia Mena, age 11, of Dallas, Texas, for her question:

What causes thunder?

A clap of thunder sounds like a resounding explosion   which is exactly what it is. It is caused by a searing flash of lightning which plows a path through the moist storm cloud. The lightning, of course, is a powerful discharge of electricity and it is very, very hot.

The streak of lightning heats a narrow path of air through the cloud. Air, like most other things, expands when hot and this slice of air is very hot indeed. It must expand, but the moist cloudy air all around it is in the way. There is only one thing the hot air can do. It explodes, bursting its prison walls with a clap of thunder.