Tina McCrain, age 10, of Asheville, N.C., for her question:

WHAT DOES BREAKING THE SOUND BARRIER MEAN?

When an airplane reaches the speed of sound, it is said to be breaking the sound  or sonic  barrier.

First to break the sound barrier was Capt. Charles Yeager of the U.S. Air Force. He made his historic flight on Oct. 14, 1947, at the controls of a Bell X 1 rocket plane.

When a plane flies at a supersonic speed, a loud noise called a sonic boom often results. The noise comes from a shock wave produced by the plane. A shock wave is a pressure disturbance that builds up around an airplane flying faster than the speed of sound. It results from a change in the air flow pattern around the plane's leading edges. Although a sonic boom can't hurt people, it has been known to break windows and crack plaster.