John Milburn, age 14, of  Vancouver, Wash., for his question:

HOW DOES AN AUTO MUFFLER WORK?

An automobile muffler is used to reduce the noise made by exhaust gases from a gasoline engine. The device passes the gases through perforated pipes called louver tubes. The tubes let the gases expand and cool so that they do not produce a loud noise when they reach the outside air.

Resonating chambers located at each end of the muffler also help to deaden exhaust noise by absorbing some of the sound produced by the gases as they flow through the muffler.

Heat and pressure inside the engine's cylinders, where exhaust gases originate, are much greater than the heat and pressure of the outside air. If the exhaust gases went directly into the outside air, the sudden change would create a loud, sharp sound.