# If a bullet was singing a song, what would the shock wave sound like?

1. Jul 22, 2011

### absolom

I'm trying to wrap my head around shock waves produced by bullets and their properties.

In particular I'm interested in what affects the duration of the shock wave in time. Say someone shoots at me, the bullet passes near me, and I hear the shock wave produced by the bullet. If you look at the air pressure over time where I observe the shock wave, what might it look like, and how long in time does it last? Does this depend on the shape of the bullet? its speed? what else?

I've tried to research this question but almost all the information I can find describes the wave front of the shock wave, mainly its shape, but nothing about what happens right behind the wave front.

Another scenario which I can't seem to come up with an answer to. If a bullet was singing a song, starting right when it leaves the gun, what am I going to hear as the bullet flies by me?

2. Jul 22, 2011

### Trevormbarker

im not sure about the first question, but for the question about the singing, it depends if the bullet is ultrasonic or subsonic. If it is Subsonic then you would hear the start of the song BEFORE the bullet reaches you, if it is ultrasonic you would hear the start of the song AFTER the bullet passed you.
edit: for your first question you should be able to look up sonic booms and the sound berrior as the bullet would also experience that, and thats what the shockwave is as the bullet passes through the sound berrior it passes through the higher pressure air infront of it.

3. Jul 22, 2011

### Pythagorean

Shockwaves:

at the source of an explosive event, air is pushed away, but now there's a vacuum, so the air rushes back in to fill it. From each of these events, the wave propagates out (so you get the peak, followed by the rarefaction, a classic "N" wave signal).

You can look up the "Friedlander Waveform" for more information on equation as a function of time.

Doppler Shift:

for a bullet traveling towards you, each peak of the wave would appear to pass you faster (compared to the reference frame of the bullet) making it seem like the bullet was singing in a higher voice.

As the bullet heads away from you, the peak of each wave passes you slower, making it appear as if the bullet has a lower voice.

Last edited: Jul 22, 2011