An airplane makes a sonic boom when it’s flying faster than the speed of sound.
Sound is produced by vibrations in the air around our planet. The speed of sound at sea level is just over 12 hundred kilometers (760 miles) per hour. But this speed can vary a little under different conditions of altitude, temperature and wind. The speed of sound in air is sometimes called Mach 1, for Ernst Mach, a physicist. You hear a sonic boom when an airplane travels at Mach 1.
To understand why, imagine a speedboat on the water. It leaves a pattern of waves behind it in a large V shape. In the same way, an airplane moving faster than sound generates a V-shaped wave in the air, called a shock wave. Whenever this shock wave reaches you, you hear the boom.
When an airplane tries to travel faster than sound, a wave of compressed air builds up ahead of the plane. That’s why the speed of sound proved to be a formidable barrier to pilots. As they approached it, their aircrafts’ controls would lock or freeze.
The pilots themselves began speaking of a “sonic wall” or “sound barrier” that no one had crossed. Chuck Yeager was the first to break the sound barrier – to travel faster than sound – in the year 1947.
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