If you are moving at the speed of sound (which is approximately 343 meters per second in dry air at 20 degrees Celsius), and you play a sound behind you, an interesting phenomenon known as "Doppler effect" comes into play.
The Doppler effect describes the perceived change in frequency or pitch of a wave when there is relative motion between the source of the wave and an observer. It applies to all types of waves, including sound waves.
When you are moving at the speed of sound, and the sound source is behind you, the following happens:
Compressed Waves: As you move towards the sound source, you are effectively "chasing" the sound waves. This results in the sound waves becoming compressed or "bunched up" in front of you. The wavelength of the sound waves appears shorter, leading to a higher frequency or pitch.
Expanded Waves: On the other hand, as you move away from the sound source, the sound waves get stretched out or "spread out" behind you. The wavelength of the sound waves appears longer, resulting in a lower frequency or pitch.
In summary, if you play a sound behind you while moving at the speed of sound:
- The frequency or pitch of the sound waves will appear higher as you move towards the sound source.
- The frequency or pitch of the sound waves will appear lower as you move away from the sound source.
It's important to note that reaching the speed of sound is not practically achievable for most objects, and it is not recommended to attempt to move at such high speeds due to the risks involved. The explanation above assumes a hypothetical scenario for illustrative purposes.