Photo: guillermomadrid (flickr)
When a speed boat moves through water, it creates waves you can see. Planes create similar waves in the air, which you can hear.
Sound Waves And Airplanes
As a plane travels, it compresses air molecules in front of it, creating waves that spread in all directions. These waves travel at the speed of sound and are known as sound waves.
When a plane itself approaches the speed of sound, which is roughly 768 miles per hour, it begins to move as fast as the sound waves it is creating. When the plane moves faster than its own sound waves, it forces those waves to pile up one on top of another.
This concentration of sound waves becomes what is known as a shock wave. Shock waves are powerful waves that travel in all directions, including toward the ground. At each location where shock waves hit the ground, we hear a sonic boom.
The sonic boom is not just a one-time result of breaking the sound barrier. Because the plane is creating shock waves the entire time it flies at supersonic speeds, sonic booms can be heard the entire time as well.
Next time on A Moment of Science, we will look at how the size and altitude of a plane influence the intensity and duration of the sonic boom.