Would you hear a sonic boom from fists?

[Crescent Pulsar R]

Since I eventually plan to write a crossover with Ranma 1/2 and Gold Digger, there has been one thing that I haven't been able to reconcile between the two: punching speed, and its effect upon being faster than the speed of sound. I should be sure regarding whether Brittany created a sonic boom in the canon (since I only started reading Gold Digger this week), but it doesn't seem like I absorbed that information well enough to be. I know that the popper of a whip breaks the speed of sound, and that you can hear the result. I know that bullets also exceed the speed of sound, yet I don't ever recall there being anything that could remotely be described as a "boom" (or, in the case of a whip, a "crack") that could be heard. But would a fist, or the motion of the arm at such speeds in general (disregarding clothing or other additions to the hand and/or arm), produce any significant noise, much less the kind of effect that you'd expect from a jet flying faster than the speed of sound while near to the ground? From what I know (so far), Brittany can punch at least two times a second (it's suggested that she can do more, but the two are definite while anything above is left open to speculation), and Ranma can punch at least two-hundred times (the baseline of "hundreds" and "few hundred") in the time it takes for it to look like a single punch.

[Wyrd]

Yes. The motion of their fists would create a high pressure wave while creating a low pressure wave in its wake. This would create quite a loud boom, far greater than a whip's, but vastly less than a jet's. Part of the reason a jet's sonic boom is so loud is that it is generating a lot of noise that stays with the jet, building up in intensity until it manages to start outrunning the sound. This means that a jet never cruises at the speed of sound, it passes through it as fast as possible, because of the extreme turbulence that builds up if it stays at that speed for any length of time. It continues to generate a lot of noise as its motion compresses the sound coming off of it, greatly enhancing the amplitude of it. The tendency in fanfics to describe the amaguriken as sounding like a machine gun is not that far off, though the noise would be from the constant backwards and forwards motion of his hands as they repeatedly break through the sound barrier more than it would be from the actual impacts, though I'm sure those would add their share of noise to the situation.

[Spokavriel]

I say no just because relatively speaking the surface area of the arm and length of travel no matter how fast doesn't provide enough area to create an audible boom unless the whole body is in motion as well and even then it would be a boom from the wake of all of the puncher not just the fist.

Betatech is a bit different.

[Wray Loflin]

Yes it would, the size or area of an object doesn't matter a lot. Consider cracking a whip it is not the whole whip that makes the crack, it is the end of the whip breaking the sound barrier. The whole whip is not going faster than the speed of sound just the end.

[Spokavriel]

The length of travel is the factor of importance in comparison there. There is allot of relativity involved though. And I really am having trouble trying to convert what I am thinking into something I can type out. I really don't want to try to do it as a math formula because I know I wouldn't get it right that way anyway.

[Wyrd]

Most of the noise from a gun or whip comes entirely from motion. A normal fist is not going to be able to make much noise, but that is because a normal fist can't go that fast. A whip works by taking a high amplitude but low frequency wave at the handle that compresses to a low amplitude high frequency wave by the time it reaches the tip, accelerating the tip enough to create a tiny pressure wave that makes a lot of noise. The increased surface area of a fist moving at the same speeds would produce a much louder sound. In essence, the speed determines the frequency of the sound and the surface area determines the amplitude. Actually, thinking about it that way, the fact that Ranma does so many punches in such a short time might make a very high pitched noise or a very loud hum(120 plus decibels) instead of a series of pops like machine gun fire.

Think of a speaker, especially the really big variety, which you can actually see move. They produce sound by pushing a little bit forward and then pulling a little bit back, creating higher frequencies by moving faster and higher amplitudes by moving further. As Ranma punches, his arm is moving several feet, which should produce one heck of a load noise, and doing so with a regular rhythm, giving that noise a distinct sound based on exactly how fast he is punching.

[Spokavriel]

Speaker frequencies is where the math in the way of trying to articulate myself got into my head from. But also take into account the full travel arc of Ranma's reach It has to repeatedly pass through that area for his chestnut fist. And the Speed of sound is actually higher in ground velocity at sea level than it is at altitude. Its been proven. That is another factor. And like I said my mind repeatedly goes back to equations.

[Ellen Kuhfeld]

Bullets make a definite sonic boom. They're mostly supersonic these days http://en.wikipedia.org/wiki/Bullet_bow_shockwave. In fact, a silencer (or suppressor) doesn't work on a gun that fires supersonic bullets -- http://en.wikipedia.org/wiki/Suppressor. So when quiet is needed, they use subsonic bullets.

A fist pushes around a lot more air than a bullet. On the other hand, if we are doing amaguriken, we'll put out maybe 200 punches per second. Assume the fist travels a foot and a half out, and a foot and a half back, that's 3*200 = 600 feet per second. The speed of sound at sea level is around 1100 feet per second. I wouldn't really hope for sonic booms.

[Spokavriel]

I guess my #1 reason for saying No it wouldn't comes down to the fact that in the amiguriken his arm is returning back through the same air space. In the case of the whip or bullet or really anything that produces a boom you do not have it immediately reversing through the same space of destabilized air and that is where most of the chaos cluttering my thought process on this fits in. Basically as the compression gets sufficient for the boom all of a sudden its hit by a vacuum because the arm reversed. I think the limited travel space and repetition would make it so that you are more likely to end up with sounds that build up before collapsing on the air if that makes any sense. Or it would be exponentially more velocity needed due to the reduced travel zone.

[Crescent Pulsar R]

Say, if his arm did move through the same space with each complete execution (forward and backward), and it was fast enough to sustain a vacuum within that space... would his arm be victim to decompression? @_@

[Ellen Kuhfeld]

Say, if his arm did move through the same space with each complete execution (forward and backward), and it was fast enough to sustain a vacuum within that space... would his arm be victim to decompression? @_@

If he can use his ki to protect his bones from all those impacts, decompression would be easy meat.

[Spokavriel]

If the skin on his hand doesn't burst when he hits concrete it can probably take the vacuum for a while. Heck NASA did a few tests and the human body could probably take 10 min of hard vacuum if you could survive without the air.

[Wyrd]

I guess my #1 reason for saying No it wouldn't comes down to the fact that in the amiguriken his arm is returning back through the same air space. In the case of the whip or bullet or really anything that produces a boom you do not have it immediately reversing through the same space of destabilized air and that is where most of the chaos cluttering my thought process on this fits in. Basically as the compression gets sufficient for the boom all of a sudden its hit by a vacuum because the arm reversed. I think the limited travel space and repetition would make it so that you are more likely to end up with sounds that build up before collapsing on the air if that makes any sense. Or it would be exponentially more velocity needed due to the reduced travel zone.

Actually, the pull back just creates the downswing of the wave. A sound wave is an area of compression surrounded by areas of decompression. The low points of a sonic wave pattern will usually have a lower air pressure than the medium they are travelling through. That is the nature of that variety of wave. After all, a speaker works by pushing and pulling in the same very small space. It is possible that a fast series of punches would effectively create a solid area in the area his fist is passing through where no air is able to enter to be compressed into sound waves. By this point, the frequency of any sound he was producing would have moved far beyond the hearing range of humans and possibly started doing structural damage to his surroundings, such as liquefying the bones of any spectators, but that level of speed is theoretically possible, especially when dealing with an over the top fantasy setting.

Say, if his arm did move through the same space with each complete execution (forward and backward), and it was fast enough to sustain a vacuum within that space... would his arm be victim to decompression? @_@

No. His arm is pressing the air out of the way to create the vaccuum, so it is actually experiencing very high pressure. It doesn't have time to notice the drop in pressure while moving away from the air before it is back to push any encroaching air back out of the way.

A fist pushes around a lot more air than a bullet. On the other hand, if we are doing amaguriken, we'll put out maybe 200 punches per second. Assume the fist travels a foot and a half out, and a foot and a half back, that's 3*200 = 600 feet per second. The speed of sound at sea level is around 1100 feet per second. I wouldn't really hope for sonic booms.

Ah, but the question was specifically about punches that did break the speed of sound. Even if the canon technique is not fast enough for that to be an issue, it does not negate the purpose of the question.

edit: I'm having fun with this discussion. Last time I enjoyed a debate this much was a time travel thread over on the Sailor Ranko forums.

[Crescent Pulsar R]

I very much like the responses I've gotten for this. It's way out of my depth, but of what I can follow I find interesting and insightful. Or maybe I'm a sucker for discussions that bring canon science-fiction and science-non-fiction together.

Speaking of canon... In regard to Ranma 1/2, perhaps there's skill to the subtlety behind the speedy hands that make no discernible sound nor disturbance. I mean, if not, the length of one's arm will likely put the user at as much risk as the person it's being used on. And there are so many useful applications for sneaky hands that aren't noticed... *Points to Happosai and Genma*

[mondu_the_fat]

Guile says yes.

Anyway, part of the reason why planes go boom while whips crack is doppler.

http://en.wikipedia.org/wiki/Doppler_effect

By the time you hear a plane's boom, its already heading AWAY from you, which results in a lower frequency sound. If the plane is heading towards you, perpendicular to you or is near you, it would sound like a crack.

http://en.wikipedia.org/wiki/Sonic_boom

A sonic boom is usually heard as a deep double "boom" as the aircraft is usually some distance away. However, as those who have witnessed landings of space shuttles have heard, when the aircraft is nearby the sonic boom is a sharper "bang" or "crack"

Unless the whip wielder (or puncher) is on a sufficiently fast vehicle heading away from the person hearing the sound, the sound will be a crack.

Say, if his arm did move through the same space with each complete execution (forward and backward), and it was fast enough to sustain a vacuum within that space... would his arm be victim to decompression?

Despite what comics and movies (I'm looking at you, Total Recall) might suggest, bodies don't bulge out and explode in a vacuum. A person would die by asphyxiation first, and even that requires full body vacuum. Even "explosive decompression" isn't really "explosive".

http://imagine.gsfc.nasa.gov/docs/ask_a ... 70603.html
http://www.geoffreylandis.com/vacuum.html
http://www.aerospaceweb.org/question/at ... 0291.shtml

it is also worthwhile to explain those a person will not experience. A body or head does not explode, as sometimes shown in movies and television programs, because skin and bones have enough strength to contain the higher pressure fluids within the body and prevent them from escaping outward.