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You know the typical wind slash in anime or games where the swordsman slashes from afar either vertically or horizontally and the wind pressure or projectile cut the opponent, like in this image for example.

Now I wonder if this is scientifically possible, or is there a solution for it? and What mechanism for the sword or the weapon shape to achieve such a state? How much strength or speed would the person need to swing his arm to manage so(I know a normal human won't reach it or his hand or body will rip apart just by common sense alone), what are the side effects, and what would the wind cut/slash look like?

I know there are some recent similar questions like Fencing style for blades that can attack from a distance but he/she mostly asking for the martial art, not how to achieve such projections.

enter image description here

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    $\begingroup$ I don't know about slashing, but a burst of air that causes impact damage seems possible if you could make a more powerful version of the air bazooka toy. It seems all you need is a tube and a plunger. Even the toy version that just uses a little band can deliver quite a bit of force from a few 10s of feet. If the plunger was powerful enough you could probably get a lot of force. $\endgroup$
    – user4574
    Commented Apr 7, 2019 at 14:05
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    $\begingroup$ I'm going to have to think about this one. Offhand, an "air blade" wont be able to cut anything. However, I am going to have to think about whether an air vortex can drill into something. Vortexes have the advantage of keeping power localized. I'm just not sure what happens when a vortex tries to go supersonic. $\endgroup$
    – Cort Ammon
    Commented Apr 7, 2019 at 14:37
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    $\begingroup$ You really need something moving at supersonic speeds, really close. E.g. Thrust SSC or jet fighter making low pass. $\endgroup$
    – jamesqf
    Commented Apr 7, 2019 at 17:41
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    $\begingroup$ Probably the closest real thing but still not really close: en.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech $\endgroup$
    – Ville Niemi
    Commented Apr 7, 2019 at 18:21
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    $\begingroup$ As in the above is what would happen if you attached your katana to a gas turbine so that it rotates at supersonic speed. Note the reported side effects. $\endgroup$
    – Ville Niemi
    Commented Apr 7, 2019 at 18:23

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Not possible without also ejecting particulate matter. If it could be done then people would be cut into pieces by standing near a helicopter or aircraft propeller.

The only solution would be to use sand or shot blasting. Even then, if your opponent was wearing armour, the worst you are likely to do is clean it for them.

enter image description here

You would also require quite a lot of equipment.

enter image description here

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    $\begingroup$ Just to add to your answer, a sand blaster type weapon could easily harm someone in armour if pointed at their helmet. It would go in between the gaps in the eye slits if they were wearing a closed face helmet. I know that i, for one, would not want highly pressurised sand fired into my eyes. If they were in an open face helmet... yeah, i dont think they are going to have a good time at all. If you used metal fillings instead, it might cause lacerations or if you used a powder it could cause someone to choke as they inhaled it. $\endgroup$
    – Liam Morris
    Commented Apr 7, 2019 at 9:33
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    $\begingroup$ @LiamMorris heck, with enough pressure, you can use water and the guy won't see again. $\endgroup$
    – John Dvorak
    Commented Apr 7, 2019 at 13:58
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    $\begingroup$ @JohnDvorak You could yes, you could even put gravel or sand in with it and then you’ve got yourself a water cutter, at close range they can cut through steel. $\endgroup$
    – Liam Morris
    Commented Apr 7, 2019 at 14:03
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    $\begingroup$ This does not look as magical as it is supposed to be! $\endgroup$
    – Battle
    Commented Apr 8, 2019 at 5:53
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    $\begingroup$ @Battle - The tags for the question are science and physics. No request for magic! $\endgroup$
    – chasly - supports Monica
    Commented Apr 8, 2019 at 8:07
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It is possible to kill with air pressure, you just have to be REALLY CLOSE to do it

The only documented death I found from "air pressure" is Jon-Erik Hexum, who was bored on the set of his tv series. He had a gun loaded with blanks, and decided to play a fake game of Russian Roulette with his gun and the blank cartridges (i.e. put the gun on your temple and pull the trigger).

This is still not safe because of both the explosion created by the blank and the bits of paper and plastic moving at high speeds out of the muzzle. He died from a fractured skull and pieces of paper and plastic that were embedded in his brain.

Blanks cause injuries if put next to the skin.

Of course, millions of actors have been "shot" by blanks with no ill effects. Most on-set fatalities involved a malfunctioning or poorly maintained gun, such as Brandon Lee.

To sum up - It is completely possible to cause injury or death with air pressure, but the death zone is basically touching the other person. Anyone with a sword could simply cut off the hand holding the "air sword", so this weapon would be completely impractical.

One other thing to consider. Blanks are meant to be a safe way to fire a gun on-screen. Real bullets came first. If you have the tech to get air moving at the speed required to injure or kill, you already have the technology to make a real gun that fires real projectiles.

EDIT:

Commenters pointed out that a shock-wave from an explosion (i.e. air pressure) can kill. This was proven repeatedly on MythBusters, which also tested Hollywood cliches for survivability. Simply jumping behind a wooden table (according to the show) is enough to protect you from the blast.

Blast-waves can kill but are even more impractical than an "air sword". Why...

1) The attacker will be at the epicenter of the blast. They will likely be more injured than the victim.

2) Simply running away or jumping behind a wooden table would protect the victim

3) (Same as blanks) If you have the tech to get here, then you can make a grenade, which is obviously deadly.

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    $\begingroup$ "millions of actors have been "shot" by blanks" ... thousands maybe? $\endgroup$
    – Daniel P
    Commented Apr 8, 2019 at 13:48
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    $\begingroup$ Anyone killed by the concussive effects of bombs and artillery was killed by air pressure. $\endgroup$
    – StackOverthrow
    Commented Apr 8, 2019 at 16:44
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    $\begingroup$ @TKK - addressed why exploding shockwaves are impractical as well $\endgroup$
    – sevensevens
    Commented Apr 8, 2019 at 21:06
  • $\begingroup$ Note focused shockwaves like those produced by a shaped charge can achieve more distance but no way to create one with anything like a blade. $\endgroup$
    – John
    Commented May 28, 2021 at 5:19
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No, especially not slashing.

Punching bags can really take a beating because the sand inside absorbs the blows. The incoming blow slams straight into the side of the bag, which directly transfers that energy into the sand inside. The first layer of sand broadcasts that energy to the sand above, below, and beside. As each "layer" of sand transfers energy to the next layer, it diffuses that energy, spreading it outward from where your first originally struck. Not only that, but there are little gaps between the grains of sand, and as the sand slips and jostles, it burns the energy it was given on friction. Thus, even a strong punch will only lightly shift the sand in the bag, and even that will just shift back a second later as the bag settles.

But what does sand have to do with air?

Well, air is like the sand in the bag - except that air molecules have even more distance between them. A "sharp" blast of air will be barely a breeze a step away. Air focused in a tiny stream will quickly push outward, expanding into the lower pressure space in front of it. As it expands, it carries less and less energy - what used to be millions of molecules traveling together quickly becomes thousands, or tens. The amount of air it would take to actually hurt someone would be immense, even at shorter-than-pocket-knife range.

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This is just kind of related, but it might interest you that there is a small crab or shrimp that launches sonic/shock waves with their claws: https://www.youtube.com/watch?v=XC6I8iPiHT8 (also quite cute!))

The main ingredient of this effect seems to be a delicate buildup and release of pressure, giving you an idea how envision physically sound way to weaponize "air slashes": https://en.wikipedia.org/wiki/Alpheidae#Snapping_effect

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    $\begingroup$ It is worth noting that this won't work in air. See e.g. worldbuilding.stackexchange.com/questions/52292/… $\endgroup$
    – Alex bGoode
    Commented Apr 8, 2019 at 11:12
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    $\begingroup$ I mean, those are cavitation bubbles. Those are bubbles of vacuum created when something moves fast enough that water takes a moment to fill the space back up. Still neat, but air pressure isn't going to have enough force to do anything. $\endgroup$
    – David
    Commented Apr 8, 2019 at 12:36
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    $\begingroup$ @David Cavitation produces bubbles of low-pressure vapor, not bubbles of vacuum. A sharp drop in pressure causes a small bubble of liquid to vaporize, which collapses very quickly. As Alex points out, you can't cavitate a gas because it's already a vapor. $\endgroup$
    – Nuclear Hoagie
    Commented Apr 8, 2019 at 18:20
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No, its not really possible.

Sound is just a pressure wave. If you have a powerful enough sound wave, it can do some damage.

Loudest possible sound wave is 194 decibels. This is a result of the wave trough being a vacuum (and the wave crest being 2 atm.)

This sound level is considered approximately the level required to be fatal. Human studies are necessarily restricted. It is thought that this sound level could induce fatal embolisms in the lungs.

Since flesh has considerable flexibility, it is resilient against sonic assault. Something rigid like glass or concrete would be more easily damaged, and can in fact be destroyed when a frequency closely match to a natural vibration mode is used. This is not a sonic cutting attack though.

194 Db is not powerful enough to cut flesh. So, you cannot use a cutting sound strike no matter how you wave your weapon. In theory, if your weapon was large enough, and moving fast enough, it could be sufficient to cause damage due to hearing hearing loss, or even a stunning effect, but never cut flesh.

Why do I go the sound route? Because you cannot cut with a wind at a distance. Up close, a compressed air can easily cut human flesh. But at a distance, the compressed air expands rapidly and can no long be a cutting tool (nothing is sharp any more at a distance). Previous answers mention this in some form.

Sound can be focused and could represent a possible cutting tool operating at a distance, but it is just not strong enough to cut.

I used to work in noise control technology, so I am perhaps more attuned to sound applications.

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    $\begingroup$ This assumes you're merely creating a sound wave. But supposed you were ejecting a slice of air at relativistic speeds? $\endgroup$
    – Shufflepants
    Commented Apr 8, 2019 at 14:53
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    $\begingroup$ I suspect "ejecting air at relativistic speeds" is going to just cause a loud bang and a flash basically wherever it's accelerated as the fast air's kinetic energy turns into thermal energy and plasma on contact with the normal, just-chillin'-there air. $\endgroup$
    – William
    Commented Apr 8, 2019 at 19:31
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As pointed out in the adjoining replies, a blast/slash of air cannot occur on its own, from a physical viewpoint. You can either compress that air and direct it at the target and this would require insanely high precision to focus it and cause significant damage. Also, as the other reply states, "air slashes" are basically shock waves travelling in air. Now, from my knowledge of undergraduate fluid mechanics, a shock wave occurs when a fluid is made to undergo a careful transition from subsonic state to supersonic state by making it flow through a convergent-divergent nozzle. In order to create the shock wave at the exit plane of the nozzle (which literally is your weapon), you need to operate it very precisely under the "third design pressure ratio point" which, in practice, is too difficult to achieve. Also, once the shock wave exits the nozzle, it can no longer be treated as a one-dimensional wavefront, rather it becomes three-dimensional, expanding and dissipating exponentially. So, that would require your opponent to be present within a few meters of your reach.

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    $\begingroup$ Hi, welcome to Worldbuilding.SE! Please take the time to vist out Tour page if you havent already. $\endgroup$
    – Liam Morris
    Commented Apr 7, 2019 at 17:52
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A metal cutting water jet shoots at 760 m/s you could attach one to your sword.

Speed of sound 343 m/s if your character arm can move that fast then it would be deadly. (why not just use throwing weapon or a gun)

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    $\begingroup$ well this is just quriousity how to make wind cut/slash posible not the practicality or alternative although the wind contain sand or other substance that can make it happen is aceptable to me, but unfortunately i consider water jet is an alternative not really wind base except maybe if the water vapour or the subtance can do such reaction, and at least i think for melee weapon it can be a surprise attack against opponent that stay out of range of the melee weapon. besides i can just make the world dont have gun or long range weapon because of tradition. $\endgroup$
    – Li Jun
    Commented Apr 7, 2019 at 10:37
  • $\begingroup$ since i cant edit it anymore just to be more clear: i mean the wind contain small sand or dust or other small particle substance that can make it happen is aceptable to me, but unfortunately i consider water jet is an alternative not really wind base to me except maybe if the water vapour or the small subtance can still do such reaction. $\endgroup$
    – Li Jun
    Commented Apr 7, 2019 at 10:57
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    $\begingroup$ Waterjust are dangerous at point-blank range, but I think their effectiveness drops off very quickly so they're not much good as ranged weapons. Waterjets were at one time considered for antitank "melee" weapons varried by infantry, but were (and I think still are) too big and heavy for practical use. Might not always be that way, of course... $\endgroup$
    – Starfish Prime
    Commented Apr 7, 2019 at 12:45
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    $\begingroup$ I don't see how a water jet qualifies as wind. $\endgroup$
    – L.Dutch ♦
    Commented Apr 7, 2019 at 12:51
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This is very far-fetched, but at least sort-of based in real science.

A magnifying glass can concentrate sunlight enough to start a fire.

Lithotripsy is a medical procedure where shock waves are passed through the body of the patient at different angles so that they target kidney stones, causing them to break apart. The shock waves are designed to come to a focal point centered on the stones to mimimize damage to other tissue. The same concept is applied in some forms of radiation therapy.

A whispering gallery is a room or environment which takes advantage of the reflection of sound from curved walls to allow soft sounds to be heard far away. In some cases an ellipsoidal chamber is used. A very faint sound made at one focal point reflects from the curved walls and can be heard clearly at the other focal point, even though it can't be heard in other parts of the chamber.

Imagine combining these concepts in a special environment such that a series of loud sounds generated at one point echo through a chamber, and are timed so perfectly that the multiple echoes all arrive at a single point simultaneously, producing a very small but intense sound, possibly enough to cause injury.

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A wind with maximum sharpness is a discontinuity - where the velocity suddenly changes between different regions of air, rather than continuously (gradually) changing from one velocity to another.

I don't know how dangerous air shock waves are, but water shock waves can klll you underwater. Probably, a sufficiently strong air shock wave (i.e. large enough change in velocity) will be as deadly as you want.

Shockwaves are commonly spherical, heading out in all directions from a point, but I think some directionality must be possible, just as sound wave and light waves can have some directionality. Perhaps, originating from within a pipe?

However, a shock wave generated by a sword slashing (extremely quickly) would travel laterally to the sword - like the bow wave of a ship. A force-push (extremely quickly) might work better.

\disclaimer all off the top of my head, not an expert

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    $\begingroup$ I believe ‘air shockwaves’ are what kills you during an explosion, pressure builds up in a container before bursting through, creating shockwaves. I think that the Mythbusters demonstrated that shockwaves in air are move deadly than those in water. In water, there is more material the shockwave needs to move in order to reach you, reducing its force. $\endgroup$
    – Liam Morris
    Commented Apr 8, 2019 at 8:33
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    $\begingroup$ @LiamMorris - I think you've got it backwards. Sound - and other forms of pressure waves, such as those from an explosion - travel much better in water because it's nearly incompressible. You might be mixing up the concussive vs shrapnel aspects of, for example, a grenade. Shrapnel won't go far underwater, but the shockwave will be lethal to a person underwater at much greater range. For a visceral demonstration of this, check out youtube.com/watch?v=W4DnuQOtA8E $\endgroup$
    – William
    Commented Apr 8, 2019 at 19:36
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    $\begingroup$ @William-Rem Ah that must be it then, i’ve mixed up the concusive force and the shockwave, i thought they were the same. I know sound travels further in water due to the increased number of particles to vibrate. To be honest, i did have a little voice in the back of my mind telling me thats not quite right as i was writing it but, as i say, i thought the two were the same thing so did not know what else to call it. $\endgroup$
    – Liam Morris
    Commented Apr 8, 2019 at 19:46
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Yes, it is possible. How you you do it? You attach a shaped charge explosibe to your sword. A bomb's shock wave, when properly shaped, is certainly capable of cutting people, and the medium for the shock wave is the air between the bomb and its target.

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I know this is a physics/science question, but I think the "mechanism" used in the anime situations you're describing is magic. A lot of martial arts (and especially kung fu) fiction invokes some kind of magical element, like the flying in Crouching Tiger, Hidden Dragon (2000). Kung Fu Panda 3 (2016) explains it as "ch'i" which is a concept used by real-life martial arts teachers to get students thinking about energy flowing through their bodies, but fiction usually takes the concept to a fantastically supernatural level. The idea of cutting at a distance isn't so different from a voodoo doll situation, and is seen in movies like Kung Fu Hustle (2004) by means of a magical stringed instrument rather than any kind of cutting implement. There's no reason to think the air is actually what's doing the cutting by itself.

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    $\begingroup$ Welcome to the site, Kyle. Please note that this question is specifically asking for a science-based solution to a seemingly magical effect. As such, providing an answer that says "use magic" doesn't satisfy the needs of the asker and is likely to result in the deletion of the answer for not answering the question that was asked. If you haven't already, feel free to take the tour and check out our site culture to get a better understanding of the site. $\endgroup$
    – Frostfyre
    Commented Apr 8, 2019 at 19:28
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    $\begingroup$ Thank you for the welcome message, @Frostfyre, as those links are very helpful. I don't know that I was actually saying to use magic. Perhaps I miscommunicated, but my intent was more along the lines of elaborating on why it's "impossible" as other answers have stated. And while the question is certainly asking for a scientific solution, I don't see anything that says magic is off the table. But of course I'll take your word for it if there's a sort of commonly understood subtext in the culture here. $\endgroup$
    – Kyle Delaney
    Commented Apr 8, 2019 at 19:39
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    $\begingroup$ Hi Kyle, welcome. Yeah, the subtext is that it's a question about something we all understand to be fiction, asking if there is a context in which it could be real. The author says "I wonder if this is scientifically possible." We have a lot of questions like that (which are on topic, whether the answer is yes or no) so those of us who have hung out for a while are used to them and see them clearly. But new folks like you aren't familiar with the stack yet and we understand that. $\endgroup$
    – Cyn
    Commented Apr 8, 2019 at 22:25
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    $\begingroup$ Hello Kyle. We do allow frame challenges, meaning you disagree with the question's premise and can provide an alternative. However, it's expected that you explain why the premise is implausible. $\endgroup$
    – JBH
    Commented Apr 8, 2019 at 22:35
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The reason why air doesn't cut in an atmosphere, is because the atmosphere is able to absorb all of it. There's a lot of particles of nitrogen that can get hit by the 'gun' and then re-direct the energy in another direction. Sand blasters work because the sand has enough momentum to move the atmosphere out the way and keep the force directed in the right direction.

Water cutters used on earth are approximately 2k bar (30k psi) - and that pressure is able to cut sheet metal without issue - though they do cut slowly. If that pressure was applied by air, it would cut exactly the same (because the force on the metal is the same).

Commercial air pumps exist that are able to output air at this high pressure; they're not small. You'll also need to store quite a significant amount of gas to use this device too - so realistically, you're not going to have it on your person. You can however run a pipe from the pump to the weapon.

The range will still be limited as the particles in the beam will still spread out - but no where near as limited on earth; but I wouldn't want to be within a few meters of the front of this weapon. Especially as it doesn't actually need to do very much damage to someones space suit/craft to result in a leak.

Given the number of anime programs that are set in space with crafts that fight with swords, this seems like it is still on topic!

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I was also wondering about this point for a while..

So i don't know whether it is possible But If you were to project 2 identical walls of wind by the sides of the the sword and only keep think layer of ait by the sword and using a slash as a starting point for the wind to move and blasting another burst of air to propel it making it practically air slash through empty space

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I'd say theoretically possible? Yes. Humanly possible? No.

Hypothetically, were superman a real being, I doubt he could even slash a sword fast enough/hard enough to cause that kind of vortex/current. You'd most likely have to swing your sword at speeds upward of a billion M/S. For an idea of how fast that is, light travels at 299,792,458 m/s. So over 3x the speed of light would be my theoretical belief. (which would likely completely disintegrate the user's sword arm while giving a minor cut to their target)

I believe in anime however, the focus is the users ki, or chi. This is the life energy that exists in all things. When our ki is weak, we become sick or exhausted. When our ki is strong, we become energized. The idea in anime is that the samurai's ki is so powerful, it is able to be used as a weapon, surrounding the blade then cutting through everything in it's way.

Think of Dragon Ball and the "energy blasts" they use. Same idea here. Their ki energy is so powerful, and they are so well trained, that they can compact their energy into a blast, such as the kamehameha wave, where as the spirit bomb is made up of ki energy from everything around, not just the user, which is what makes it so powerful. Typically, the show gives the idea that the spiritbomb is made up of ki energy from everything on Earth, from plant life to humans to animals, combining all of their ki energy into a single bomb.

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    $\begingroup$ The question is tagged science based, and you propose manga-babble and going 3 times faster than the speed of light, which both fail to satisfy the requirement of being science based. $\endgroup$
    – L.Dutch ♦
    Commented Jan 14, 2020 at 6:16
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    $\begingroup$ "You'd most likely have to swing your sword at speeds upward of a billion M/S" This question is science-based, so unless you get that affirmation backed up expect to see downvotes and votes to delete your answer. $\endgroup$
    – The Square-Cube Law
    Commented Jan 14, 2020 at 17:18
  • $\begingroup$ So you guys expect someone to scientifically swing a sword fast enough to cause a vortex to cut someone? I think my answer gave plenty of info to say no, it's not scientifically possible. And it went on to explain what he's seeing in anime... Not sure what the problem is. OP himself mentioned he's asking cuz of what he's seen in anime. $\endgroup$
    – Grimm
    Commented Jan 14, 2020 at 17:34
  • $\begingroup$ As the speed of an object approaches the speed of light, the relativistic mass increases. An object going AT light speed would have an infinite amount of energy. $\endgroup$
    – Praearcturus
    Commented Jul 1, 2021 at 22:57

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