Deleted
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Post by Deleted on Aug 30, 2010 1:32:54 GMT
Ok, so a while ago me and a friend were cutting and I was explaining to him that he needs to swing the sword in the air a few times until he hears the blade whistle. I then went on to explain that the reason it whistles is that the blade is separating the air to either side of it with equal force, so that when the air collapses back onto itself, on the other side of the blade, you actually hear the collision. On the other hand, if the edge alignment is off, you are pushing more air to one side and it rolls back onto itself rather then a straight collision.
He then looks at me like I'm making things up but then proceeds to swing the sword till he hears the whistle.
So am I totally off base as to the origin of the whistle?
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Avery
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Post by Avery on Aug 30, 2010 2:18:41 GMT
That sound is called Tachikaze, which translates to "sword wind". Google that and you should find some good info to back you up.
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Post by YlliwCir on Aug 30, 2010 2:20:04 GMT
Without getting into too much of the physics, the sound originates from two sources. The first is the sword compresses the air in front of it and de-compresses the air behind it. This produces a compressional sound wave. You can do the same thing with a rope or a long stick. The second is that the sword itself acts like a "tuning fork" and vibrates perpendicular to the face of the blade. This sound will depend upon the size and shape of the sword as well as the material from which it is made.
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Post by Deleted on Aug 30, 2010 2:30:12 GMT
Doesn´t altitude and humidity enter into it too Prof ?
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Dom T.
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Post by Dom T. on Aug 30, 2010 2:35:15 GMT
Um... if it whistles, you're doing it right. If it doesn't you're doing it wrong. XD
All this talk of collisions and forces and compression and whatnot is confusing. Guess that makes me a bit simple-minded. ...And I've never had the attention-span for physics and the like.
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Post by YlliwCir on Aug 30, 2010 2:40:38 GMT
Doesn´t altitude and humidity enter into it too Prof ? Well, of course it does, Jim. As well as the air temperature and the phase of the moon.
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Post by Deleted on Aug 30, 2010 2:50:20 GMT
Doesn´t altitude and humidity enter into it too Prof ? Well, of course it does, Jim. As well as the air temperature and the phase of the moon. how about the alignment of the sun with the center of the galaxy?
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Deleted
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Post by Deleted on Aug 30, 2010 2:54:15 GMT
Air is not some sort of jello medium that "slaps" back on itself after you cut it with your mighty blade. It's a compressible fluid. All audible sound is a perception of variation in air pressure, which is most noticeable when it comes in regular waves of a high pressure-lower pressure-high pressure pattern from a specific source, all which travel at the same (generally speaking) consistent speed, the "speed of sound." The only time you would hear a "collision" of air is in a change of pressure so violent that the action and resultant expansion of pressure waves away from the source is faster than the natural speed of waves through the fluid air medium, so these high pressure zones 'catch up with each other' and collapse into an abrupt change of very high pressure back to low pressure. This happens when the source itself is moving faster than the speed of sound, so the pressure waves it leaves in its wake are running into each other (sonic boom from bullets, fighter jets, bullwhips, etc.) or when the source itself is a supersonic rapid expansion of air (the air caused to expand by a flash of lightning, high explosives, etc.) I don't think any of our swording maneuvers are capable of a violent enough movement of air for pressure waves to collapse on each other, unless you can get the tip of your blade past 770 miles an hour, though at that speed the collapse would be audible whether or not your edge alignment was proper. I think you're more in the ball park with the statements "the blade is separating the air to either side of it with equal force" and "if the edge alignment is off, you are pushing more air to one side" but again, you aren't pushing air out of the way to make a void that needs to be filled; you're creating a flowing boundary layer on either side of the blade that has a lower pressure than the air than is not next to the surface of the blade. When these flows are of a nearly equal rate on either side (proper alignment) you preserve the relative laminar flow of the fluid in question, so the quick change in pressure produced by the movement of your blade remains distinct and unmuddled, and the waves coming off of it are clear and discernible to the ear as a sharp whistle. When alignment is off, these flowing boundary layers are uneven on one side compared to the other as you move your blade through the fluid, so the pressures and speeds are all over the place in the region directly behind your blade, creating an area of turbulence that dissipates the energy of the pressure waves in swirling eddies rather than sharp distinctions in a high pressure-low pressure-high pressure pattern. It also creates a lot of drag. Hence, no whistle. I think.
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Post by Deleted on Aug 30, 2010 2:54:34 GMT
It also depends on the wielder's horoscope and Chuck Norris mood when the blade is swung ....
.... Yes.
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Deleted
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Post by Deleted on Aug 30, 2010 2:58:37 GMT
wait, luna, you mean you don't swing your sword past 770 mph?
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Post by Deleted on Aug 30, 2010 2:59:33 GMT
The first is the sword compresses the air in front of it and de-compresses the air behind it. This produces a compressional sound wave. You can do the same thing with a rope or a long stick. So in a sense, you are creating a small vacuum every time you swing a sword. The vacuum then collapses, and sound is produced. And I googled Tachikaze, but most of what came up was Anime stuff... maybe talking about space ships or something. But once I added physics and math into the search, I got more of what I was looking for. You guys may resume pseudo physics now. Don't forget barometric pressure... which now that I say that, probably does play a role into the pitch of the sound.
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Deleted
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Post by Deleted on Aug 30, 2010 3:02:58 GMT
The first is the sword compresses the air in front of it and de-compresses the air behind it. This produces a compressional sound wave. You can do the same thing with a rope or a long stick. So in a sense, you are creating a small vacuum every time you swing a sword. The vacuum then collapses, and sound is produced.. No. You are just creating two regions of differing pressure where before the air was at a pretty much homogeneous pressure.
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Deleted
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Post by Deleted on Aug 30, 2010 3:07:41 GMT
When I've had burrito's ....... I blame it on the tachikaze ..........
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Post by YlliwCir on Aug 30, 2010 3:08:34 GMT
That part I actually got from a teacher type person, Greg, right on!
That was impressive, Luna. Totally over my head yet making sound scientific sense.
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Post by chrisperoni on Aug 30, 2010 3:09:58 GMT
+1 to Lunaman aka Professor Frink- "he'll make you laugh he'll make you think"
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Deleted
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Post by Deleted on Aug 30, 2010 3:14:55 GMT
Aw, shucks. Fluid dynamics was not one of my favorite parts of physics, but some stuff sticks, you know?
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Post by Deleted on Aug 30, 2010 4:13:14 GMT
Well, I used a vacuum in a very loose sense. I meant it as an area of lower pressure and not so much the "void of air" sense. Sorry Thanks for the input Luna, you are always full of surprises!
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Deleted
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Post by Deleted on Aug 30, 2010 15:52:46 GMT
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Post by YlliwCir on Aug 30, 2010 19:23:55 GMT
I am often quite proud of how humble I have become.
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Post by randomnobody on Aug 30, 2010 19:56:28 GMT
Nicely done, Luna. I went to school, or tried to anyway, for aerodynamics and aircraft piloting and could see in my mind exactly everything that happens to air as an object, in this case a sword blade, passes through it, and all the impacts and effects and so on...but could not for anything put it into words. I do wonder often how a sword relates to an airfoil, as it's easy for me to see how a "stall" would hinder the sound of the swing. Also, PBR? Man, I haven't had that stuff since I was 10. ...I mean, uh...well, I do wonder if that's what they poured over my head at that last shop picnic in Florida... Those Air Force guys.
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