And Here Comes the Pop
Last week, we gave you the fizz, now we give you the pop. Staying with the popular sounds of the season, we thought it appropriate to dissect the pop of a champagne cork. After all, you would want to have your audiologic senses on the alert as you ring in the new year.
To get the full effect, we would want to see as well as hear the pop. Sure, we hear the sound and see the cork fly out of the bottle. But that is not all there is to see. What if we could see the sound waves produced by the pop of the cork. We can by using a special imaging technique called Schlieren imaging (Korpel, 1987). Believe it or not, by using intense light from a pinhole source, having it pass through the air disturbed by the sound waves generated by the champagne cork, and essentially stopping all the undisturbed light on a knife’s edge, one can see sound. This technique captures the optical image of the disturbed air allowing us to essentially see sound.
Equipped with our schlieren imaging set up, we create an observation field about three feet across. Imagine a square window; each side three-feet wide. The top of the champagne bottle is at the bottom right corner of the window. Ready? The explosion happens, and the first thing you see is not the cork fly off the top of the bottle. Less than a millisecond after the explosion you see high-frequency sound waves almost half way through your observation window. In about 10 ms, the sound waves have left your observation window altogether. It is not until much, much later that the champagne cork starts its flight across your observation window. In fact, it would be around 16 ms after the explosion that the cork reaches the middle of your observation window. The sound leads the cork, the oft mistaken source of the sound, by almost 15 ms (Hargather et al., 2010). There you have it. The laws of physics will remain in effect this new year’s eve; Sound will still be faster than cork – at least for the first couple of bottles.
Hargather MJ, Settles GS, Madalis MJ. (2010) Shock Waves 20: 9.
Korpel A, Mehrl D, Lin HH. (1987) Schlieren Imaging of Sound Fields. IEEE 1987 Ultrasonics Symposium, 515–518.