March 18, 2014

What is a Sonic Boom?

Hi, I’m Emerald Robinson, and in this “What Is” video, we’re going to answer the question, “What is a Sonic Boom?”

A sonic boom is the noise produced by something moving through the air faster than the speed of sound.

But how is a sonic boom produced?

As an object moves through air, it forces air molecules out of its way, creating waves. These waves move away from the object, or “propagate.” If the object moves faster than these waves can propagate, the waves become more and more compressed. Eventually they are unable get out of the way of the moving object quickly enough, and combine into one large shockwave that trails behind the object.

Sonic booms come from the shockwave created by an object moving faster than its own sound waves. The shockwave forms a cone shape around the object, with the tip of the cone at the front, and the base trailing behind. When you first see the object, it appears to be moving without making any noise. It’s only when the base of the cone reaches your ears that you hear the boom.

In order to create a sonic boom, an object must move faster than the speed of sound, about 700 miles per hour. Sometimes physicists call this speed “Mach 1.” Anything moving faster than Mach 1 is moving faster than the speed of sound.

Any object that moves faster than Mach 1 makes a sonic boom. Although we usually associate airplanes and space craft with sonic booms, meteors and other objects entering the earth’s atmosphere from space make them too. A whip’s crack is a mini-sonic boom created when its tip moves faster than the speed of sound. Even nature makes sonic booms; lightning makes air molecules move faster than the speed of sound, and causes the sonic boom we call thunder.

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