Welcome to brain Stuff from how stuff works dot com where smart Happens. Hi Am Marshall Brain with today's question, what causes a sonic boom from an airplane? You can learn a lot about sonic booms by looking at the wakes that boats leave in the water. If you toss a pebble into a pond, little waves will form in concentric circles and propagate away from the point of impact.
If a boat travels through the pond at three to five miles per hour, little waves will propagate in the same way, both ahead of and behind the boat, and the boat will travel through those little waves. If a boat travels faster than the waves can propagate through the water, then the waves can't get out of the way of the boat fast enough and they form awake. Awake is a large single wave. It's formed out of all the little waves would have propagated ahead of the boat but can't.
When an airplane travels through the air, it produces sound waves. If the plane is traveling slower than the speed of sound, which is something like seven miles per hour, then sound waves can propagate ahead of the plane. If the plane breaks the sound barrier and flies faster than the speed of sound. It produces a sonic boom when it flies past. The boom is the wake of the plane sound waves.
All of the sound waves that would have normally propagated ahead of the plane are combined together, so at first you hear nothing, and then you hear the boom that those sound waves create together. It's just like being on the shore of a smooth lake when a boat speeds passed. There's no disturbance in the water as the boat comes by, but eventually a large wave from the wake rolls onto shore.
When a plane flies passed its supersonic speeds, the exact same thing happens, but instead of a large wake wave from a boat, you get a sonic boom of sound waves from an airplane. Be sure to check out our new video podcast, Stuff from the Future. Join how Staff Work Staff as we explore the most promising and perplexing possibilities of tomorrow. The house Stuff Works iPhone app has arrived. Download it today on iTunes.