Traveling Faster than Sound
About 1 min read
As an object moves through air, it must push some of the air out of the way. But also, the object creates sound waves as it moves through the air.
As a moving source of sound, the object causes the Doppler Effect. When that object reaches the speed of sound, air cannot readily move out of the way and a shock wave is formed.
When the object is moving faster than sound, the resulting sounds travel behind the object, creating a sonic boom.
Questions you may have include:
- What is the Doppler Effect?
- What happens when the object moves at the speed of sound?
- What happens when the object moves faster than the speed of sound?
This lesson will answer those questions. Useful tool: Units Conversion
Moving in air
When an object such as an airplane moves through the air, it increases the frequency of the sound waves ahead of it, due to its velocity. This is the Doppler Effect, where the pitch of the sound is heard as higher when the object is moving toward you and the pitch is lower, as the object moves away.
At speed of sound
When the moving object or airplane reaches the speed of sound, it catches up to the sound waves it is creating, and they bunch up at the front end of the object, forming a shock wave. This is a reason that it is difficult for an airplane to break the sound barrier.
Supersonic speeds
When an aircraft travels at supersonic speeds or is moving faster than sound, it leaves the sound waves it makes behind it. These waves fan out and cause a sonic boom.
Summary
An object moving through air not only must push some of the air out of the way, but it also creates sound waves. This moving source of sound causes the Doppler Effect. When the object reaches the speed of sound, air cannot readily move out of the way and a shock wave is formed. When the object is moving faster than sound, the resulting sounds travel behind the object, creating a sonic boom.
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