I was watching one of the latest Mythbusters episodes recently when I noticed a strange phenomenon that looked oddly familiar. The experiment in question was testing the myth that a gun won’t fire in space (I.E. a perfect vacuum) something which Hollywood has a troubled past with. Whilst the answer was somewhat obvious before they began (hint: the answer, and the reasons behind it, are the same if you fired it underwater) the result was very impressive. Unfortunately I can’t find a direct link to the video however their high speed footage was nearly identical to what the Barking Dog experiment looks like, as shown in this video:
Seeing everything in slow motion is extremely interesting because it clearly shows how the sound is produced along with the characteristic light show. The flame front bouncing off the fuel saturated area pushes out the air above it, creating the sound, and as it approaches the bottom the time between those pulses rapidly decreases changing the tone of the resultant sound. In the Mythbusters episode you could see a lot of similarities although because it wasn’t an open ended system (due to the use of a vacuum) the sound produced was more of a descending low tone as the gas created by the bullet diffused and the shock wave ricocheted around.