On cracking the whip
Oct. 24th, 2006 02:44 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
beautifulduckweedA while ago, I told a friend of mine--I want to say ![[livejournal.com profile]](https://www.dreamwidth.org/img/external/lj-userinfo.gif)
theotherjay, but it might well have been somebody else--that the crack of a whip was caused by a sonic boom, i.e., the tip of the whip breaking the sound barrier. The friend was skeptical, but we didn't have ready access to any Internet tubes, so I couldn't provide any proof, just a lame protestation along the lines of "No, I swear, I read that fact from a credible source!"
Then just a few minutes ago, while dreamily contemplating the thunderstorm raging outside my office window, I thought about the speed of sound and how to calculate the distance of the lightning (it's just over a kilometer for every three seconds, since sound travels at about 340 m/s). All these musings about sonic speeds brought to mind the conversation about the whip (but obviously not the person I had it with, heh!), and what do you know, this time I had at my disposal several Internet tubes that are not at all like dump trucks, so I commandeered one of them thar tubes and dug up this article in the American Scientist about the physics behind the sound of a cracking whip.
But really, this is all an elaborate, long-winded way for me to say to that friend, whose name and face are lost in the mists of a spectacularly awful short-term memory: Neener neener, I was right, and you were a fool, a fool, for doubting me.
(OK, for serious, now: cracking a whip entails generating your own sonic boom. That is pretty goddamn cool.)
theotherjay, but it might well have been somebody else--that the crack of a whip was caused by a sonic boom, i.e., the tip of the whip breaking the sound barrier. The friend was skeptical, but we didn't have ready access to any Internet tubes, so I couldn't provide any proof, just a lame protestation along the lines of "No, I swear, I read that fact from a credible source!"Then just a few minutes ago, while dreamily contemplating the thunderstorm raging outside my office window, I thought about the speed of sound and how to calculate the distance of the lightning (it's just over a kilometer for every three seconds, since sound travels at about 340 m/s). All these musings about sonic speeds brought to mind the conversation about the whip (but obviously not the person I had it with, heh!), and what do you know, this time I had at my disposal several Internet tubes that are not at all like dump trucks, so I commandeered one of them thar tubes and dug up this article in the American Scientist about the physics behind the sound of a cracking whip.
But really, this is all an elaborate, long-winded way for me to say to that friend, whose name and face are lost in the mists of a spectacularly awful short-term memory: Neener neener, I was right, and you were a fool, a fool, for doubting me.
(OK, for serious, now: cracking a whip entails generating your own sonic boom. That is pretty goddamn cool.)
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And you didn't think to borrow my whip for this discussion?
Date: 2006-10-25 12:23 am (UTC)Re: And you didn't think to borrow my whip for this discussion?
Date: 2006-10-25 12:27 am (UTC)Re: And you didn't think to borrow my whip for this discussion?
Date: 2006-10-25 01:09 am (UTC)But if you ever want to argue it as a theory, it is not totally wrong. All sound is essentially air particles vibrating at sonic speeds, and any time an object moves faster than the waves it generates it creates a small sonic boom as the vibrations pile up (more accurately called a "shock wave" as all booms are shock waves, but not all shock waves really "boom"). Stick your finger in still water, and you will see the ripples (they will act like sound). Move the finger, and the ripples in the front pile up on themselves and create a shock wave.
An object (in this case, air escaping under pressure from between the finger and palm) moving outward will carry with it, and to some degree overcome, the waves created by the impact. The air itself will produce microaural sounds as it bumps into the stagnant air surrounding it (microaural, like microscopic. Too small to hear with the naked ear). Due to this, the air that carries the sound of the snap will to a VERY small degree radiate sound as it moves outward, so you wind up with outward radiating air from an also outward radiating source that creates outward radiating noises of its own.
From here you must graph it out, but the math basically focuses on rotational amplification, as each radiation of noise will go in all directions, and thus impact each other omniradiational expulsion of noise, creating a cyclone-like event in four dimensions (three physical, one motional/time).
The end result of this is faster and stronger vibrations than the source vibrations (stick, oh, five fingers in the water, use a tape measure. . . no, wait, three fingers and a ruler, no. . . drink three glasses of water with the ruler of Paraguay. . . Damnit. . . Drink some scotch, stick three fingers in still water, watch where the ripples collide. The collision points will be taller and wider than the rest of the ripples. When the collision points collide with other waves, they push them in such a way as to make them faster. This repeats enough times and you get really fast ripples. Now figure out a way to get your water to hover off the ground in a sphere, and stick fingers in it on all sides. . . Oh, just google it).
So you have the elements of a shock wave: Object (expanding air pushed in a sphere by other expanding air) moving faster than the sound it generates (or in this case, carries with it), creating an actual sonic boom so small it can not be heard with the naked ear.
A boom that is overcome by the sound of your finger slapping your hand :)
Re: And you didn't think to borrow my whip for this discussion?
Date: 2006-10-26 12:23 am (UTC)That was a beautifully-constructed bit off bullshit, though :) .
Re: And you didn't think to borrow my whip for this discussion?
Date: 2006-10-26 04:04 am (UTC)By the way, the constructive interfence argument is close, but no cigar. That is mostly dealing with aplitude of waves (similar to the piling up that waves do before a sonic boom, I grant), but discounts the rotational amplification inherant in four dimensional models.
Re: And you didn't think to borrow my whip for this discussion?
Date: 2006-10-26 06:45 am (UTC)Re: And you didn't think to borrow my whip for this discussion?
Date: 2006-10-26 07:53 am (UTC)Ok, for starters, since this is a theoretical (unless you have an electron microscope and a really good stopwatch handy) conversation, you have to consider both aspects seperately first, before combining them. Rotational amplification, and sound waves.
Google "Roational Amplification," and you get a ton of stuff on plasma and radio waves (remember that radio waves can not be sped up, where sound waves sort of can. Radio waves must take that amplification and translate it to greater force/volume, where slower moving masses (like air carrying sound waves) can simply be pushed faster). To grasp that a bit more, check the way a tornado develops, as outside pressure on the rotations cause them to speed up. As a mass moves through space that is pressurized by other mass (or waves, or vibrations, or smurfs. Whatever) that is also trying to move, they can collide. Except matter does not really like to collide; if far prefers to push stuff out of its way or be repelled. Hey, I just thought of a movie reference! Remember that really bad movie about a bunch of people trying to get to the earth's core? I think it was called "The Core?" I seem to recall them using multiple explosions to amplify each other. Of course, they did this to rotate a mass using expanding force rather than torque, so that is probably a bad analogy. It was the only bit of non-junk science in the entire film.
It's late. Don't expect coherence.
Damn, don't google "the core" unless you want 6,000 conspiracy theories about the world trade centers (hint: a plane hit them, and they fell over).
Ok, just google rotational amplification, or do the "sticking your fingers in water" thing and watch the waves. Each tiny expansion pushes at the edge of the rotating mass, causing it to rotate faster.
Now turn that inside out, with the high pressure at the center (the thumb and palm converging) rather than the low pressure in the center like tornadoes. Check, oh, the national weather service or something to see how tornadoes work. Ask an Okie.
So, you have the theoretical concept of rotational amplification as it applies to light and pressure. As gas moves outward under pressure it expands in all directions because there is no containing entity (other than, I suppose, the thumb and palm, taking up no more than a 30 degree cone of expansion).
Sound is a vibration that behaves in much the same way light behaves. I really, really don't feel like googling around to get examples of how sound works. So my position is "sound is a vibration that very likely acts the same as all other vibrations, in that it radiates omnidirectionally, moves at different speeds through different densities of medium, and can impact other vibrations that are identical in amplitude, orientation and frequency."
Thus, the theoretical example of whatever the hell we are talking about it either proven or disproven, depending on what position I took at the outset of this.
Going to sleep now.
no subject
Date: 2006-12-23 05:06 pm (UTC)I've heard that there are some interesting models to be found in fly-casting, as well...