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efreysson
09-06-2010, 01:47 AM
Here I go, revealing my own ignorance . . . :)

I'm planning a fantasy story with a protagonist with superhuman strength, and a huge, unbreakable sword. I'm trying to figure out how something like that would actually function.

Theoretically, what would happen if a person were struck with an indestructible sword, with more force than any real-life person can bring to bear? Would the victim be sliced in two, or would they go flying before the blade could pass all the way through? And what if the wielder struck something more durable, like a boulder? Would he cut through it, or be lifted off his feet?

Another thing I'm wondering is how to create the ultimate cutting power. Is a super-narrow edge the way to go, or does a broader one have some advantage?

Jessianodel
09-06-2010, 02:10 AM
I can't help much but I do know that a thin blade can cut hair, but it's very weak on the edge, so it can't, let's say, smash through armor.

A broader sword could smash through armor, but you might have trouble cutting paper because it's almost the same as being a blunt edge. It does a lot of crushing/mangled damage rather than clean slices.

efreysson
09-06-2010, 10:39 AM
I can't help much but I do know that a thin blade can cut hair, but it's very weak on the edge, so it can't, let's say, smash through armor.

A broader sword could smash through armor, but you might have trouble cutting paper because it's almost the same as being a blunt edge. It does a lot of crushing/mangled damage rather than clean slices.

Well yes, but I'm thinking of a fictional superstrong substance that can hold a thin edge without breaking.

Kenn
09-06-2010, 01:50 PM
In terms of the human, it would be dependent on the sharpness of the blade and the speed (not force) of the blow. A fast blow would slice and a slow heavy blow would push. The boulder would probably shatter if anything. It would be dependent on his position whether he was lifted off his feet or not (think of lifting yourself out of a chair). You want a thin blade if you want him to cut but a broad blade if you want him to smash.

Lhun
09-06-2010, 08:22 PM
Cutting has actually very little to do with sharpness. Modern ceramic knifes are sharp enough to cut glass, and harder than glass. Try to cut a wineglass with one and see what happens. The problem is that after forcing the edge of the knife/sword into the material, it has to physically push the two separated parts apart by the thickness of the knife. If you try to bend something brittle that far, it breaks. You also need the required strength to push the material apart (or break it) and simply having a sharper knife won't help at all. Having one with a very thin blade helps of course. But hitting a piece of hard, brittle material like rock with a sword that's 1 cm thick has about the same effect as you'd expect from hitting it with a round metal stick of the same thickness.

With a sword though, making it too thin (even if indestructible) will have you lose a lot of power. Since leverage is completely on the side of whatever's being hit, most of the force of the impact comes from the mass of the sword. If the sword is truly indestructible however, a 1 mm thick (or less) blade would reduce the force required to cut something probably more than enough to compensate for the lack of inertia.

If the material is not that indestructible, the optimum would be simply an up-scaled normal sword. I.e. the maximum speed you can get out of a swing has an upper limit, set by the person using it (e.g. you can't swing a 200g stick faster than a 500g stick), so pick a sword that is as heavy as possible without slowing the user down.

An unarmoured human can be cut in half (at least sideways) even by a normal person with a longsword, If it's possible to cut an armoured person completely depends on the force the superhuman can generate. Generally though, humans are too fragile to survive any narrow impact that will abruptly accelerate them enough to throw them around. A snapped spine is the very least that should be expected.

As for sharpness, about as sharp as a butter knife is all that's necessary if human-like material is the target. Making the sword sharper has almost no effect, but it won't hold an edge as well (might be a non-issue with indestructible material). Depending on the fighting style, it might be desirable to be able to grasp the edge of the sword for two-handed parries or half-sword techniques. In that case you'd want an indestructible sword to be blunt enough that it won't cut through the gloves and injure the wielder. Although the gloves could be indestructible as well of course.

Addendum: Obligatory sword sharpness demonstrations:
http://www.thearma.org/Videos/Blunt_Bastard-Sword_onBamboo.MOV
http://www.thearma.org/photos/Gathering03/G03Vids/MP4s/Blunt_cutting_7.mp4

Julie Worth
09-06-2010, 08:29 PM
Theoretically, what would happen if a person were struck with an indestructible sword, with more force than any real-life person can bring to bear? Would the victim be sliced in two, or would they go flying before the blade could pass all the way through?

You don't need an indestructible sword or superhuman strength to chop someone in two. As for people going flying, that's a movie exaggeration. Esp. when you see a person flying back from a shotgun blast. By Newton's third law, if the person is thrown back by the blast, so is the person holding the gun.

Jessianodel
09-06-2010, 10:50 PM
Well yes, but I'm thinking of a fictional superstrong substance that can hold a thin edge without breaking.

Well if it's fictional and can never break, why can't you make up your own laws? I don't understand why you're flouting certain laws of physics yet adhering to others. If it's fiction, make it up. It gives you a lot more freedom.

efreysson
09-07-2010, 02:27 AM
Well if it's fictional and can never break, why can't you make up your own laws? I don't understand why you're flouting certain laws of physics yet adhering to others. If it's fiction, make it up. It gives you a lot more freedom.

Because the way I see it, the less suspension of disbelief required to read my books, the better.





With a sword though, making it too thin (even if indestructible) will have you lose a lot of power. Since leverage is completely on the side of whatever's being hit, most of the force of the impact comes from the mass of the sword.
. . .
I.e. the maximum speed you can get out of a swing has an upper limit, set by the person using it (e.g. you can't swing a 200g stick faster than a 500g stick), so pick a sword that is as heavy as possible without slowing the user down.

So, in addition to making the sword material indestructible, I should make it super-dense and heavy too? This would give it ultimate cutting power, if swung by someone strong enough to wield it?




Generally though, humans are too fragile to survive any narrow impact that will abruptly accelerate them enough to throw them around. A snapped spine is the very least that should be expected. I'll keep this in mind.



Addendum: Obligatory sword sharpness demonstrations:
http://www.thearma.org/Videos/Blunt_Bastard-Sword_onBamboo.MOV
http://www.thearma.org/photos/Gathering03/G03Vids/MP4s/Blunt_cutting_7.mp4And how sturdy is a bamboo bundle compared to a human limb?

Smiling Ted
09-07-2010, 06:24 AM
Look up this word: monomolecular (http://en.wikipedia.org/wiki/Monomolecular_wire).

Terry L. Sanders
09-07-2010, 07:36 AM
To answer your second question first, thin is the way to go. The problem is, the thinner the blade, the less rigid and strong it will be. Imagine chopping at something with a razor blade...

Blades that will cut through anything are fairly common in science fiction, and they always involve some kind of "rubber science." Larry Niven had two variations on the theme back in the 70's. One involved the invention of a cable that was a single molecule, like a flexible crystal. Since it was one molecule, it was as thin as ANYTHING could be. Since the whole "rope" was one molecule, with inter-molecular bonds (about as strong a bond as there is outside of an atom) in an unbroken series the whole length, Sinclair molecule chain was the ultimate in strength and thin-ness.

The stuff was made for (and mostly used for) tow cables, etc. But imagine what a garrote made of the stuff would do. One molecule thick, and if you pull on it with enough force, whatever it's touching will ALWAYS give first.

The other variation he used was an alien technology that involved a force field that stopped time inside its influence. Mostly used as the ultimate suspended animation, but one of the more alien gadgets was the "variable sword"--the thinnest conductive wire possible, on a reel so you could vary the length, from scalpel to claymore and beyond--with the conductive surface acting as an antenna for a stasis field.

The "blade" was completely indestructible--nothing can break in zero time. And it was almost as thin as a Sinclair molecule chain. Ugly weapon.
*****
With real weapons, you go for the lightest, thinnest blade that won't break, bend, or flatten when you hit your target. Then you add a little bit of weight to maximize momentum when you're chopping--or add leverage (thus polearms) or both.

Most of the magic swords in real legends were "magical" because they were TOUGH. Roland's sword was called Durendal, and it's generally agreed that the word probably came from the same root as "endurance," "durable," etc. Excalibur, according to Wikipedia, is derived from a word that translates roughly as "hard cleft," and many of the derivative writers claimed it actually meant something like "cut steel."

In The Doomfarers of Coramonde, the hero finds a sword in an armory where it's been forgotten for generations--apparently because it wasn't spectacular enough in a world with flaming swords, etc. It's a fairly ordinary looking sabre that looks like downright cheap metal. A name seems to have been carved on the blade some time after it was made: BAR.

Turns out, he eventually learns, it's real name is NEVER-BLUNTED. No matter what you hit with it, or how hard, it never breaks and never loses its edge. Nothing spectacular, but nasty.
*****
If you want your superhuman to be a standard "Conan-clone," then the heavy sharp piece of steel will do, with magical backing. If you want to make him exotically nasty, you might consider something like a bill or glaive or naginata--a long, unbreakable shaft to give him lots of leverage (pretty good substitute for mass, if you do it right), with a paper-thin indestructible blade on the end. Incredibly sharp, unbreakable, and the length of the shaft would let him use his strength when he needed to. But the weapon would be so light (especially for him) that it could be incredibly fast, too. Just a thought.

Lhun
09-07-2010, 07:55 AM
So, in addition to making the sword material indestructible, I should make it super-dense and heavy too? This would give it ultimate cutting power, if swung by someone strong enough to wield it?In principle, yes.
Keep in mind though that action=reaction always applies. Swinging around a sword weighing half a ton will likely result in the character getting stuck knee deep in any ground that's not solid rock. Hitting something would not send them flying (since most of the force comes from the sword's impulse) but forcefully swinging the sword might. If the sword's around a hundred kg, that means any movement would result in the wielder being accelerated about as much as the sword (same force since action=reaction, and same acceleration since a=f/m). Being superhumanly strong doesn't make your feet stick to the ground better than a normal persons.

And how sturdy is a bamboo bundle compared to a human limb?The first one is more of a gag, to poke fun at katana-fetishists who like to claim that you need a razor-sharp japanese sword to cut bamboo.
In the second video, water soaked straw mats wrapped around a wooden stick are supposedly of similar consistency than human/animals. It's a really old setup for test cutting, and probably not too far off.
here's a dead deer: http://thearma.org/Videos/sword_test_cutting.mov

benbradley
09-07-2010, 09:32 AM
It's possible for a (not sharp) blade to throw someone without killing them. Here's video of a test flight of an early helicopter prototype:
http://www.youtube.com/watch?v=W005xnJvaSg

quicklime
09-07-2010, 07:40 PM
Here I go, revealing my own ignorance . . . :)

I'm planning a fantasy story with a protagonist with superhuman strength, and a huge, unbreakable sword. I'm trying to figure out how something like that would actually function.

Theoretically, what would happen if a person were struck with an indestructible sword, with more force than any real-life person can bring to bear? Would the victim be sliced in two, or would they go flying before the blade could pass all the way through? And what if the wielder struck something more durable, like a boulder? Would he cut through it, or be lifted off his feet?

Another thing I'm wondering is how to create the ultimate cutting power. Is a super-narrow edge the way to go, or does a broader one have some advantage?


you should request a catalog from museum replicas and browse their descriptions.

many bodies were recovered from "swordfighting times" and battlefields of the middle ages with severed legs, a bigger sword and person could cut through someone else I'm sure. armor makes it much harder and increases the likelihood a strike would "punt" them instead of slicing them. Thin blades slice better but break and dull faster; if you're making some fake metal this would be a nonissue and no reason not to keep a razor edge, as it would not dull.

Lhun
09-07-2010, 07:56 PM
It's possible for a (not sharp) blade to throw someone without killing them. Here's video of a test flight of an early helicopter prototype:
http://www.youtube.com/watch?v=W005xnJvaSgHe got thrown into the middle of the rotor, where the blades move much slower than at the edge. I still wouldn't bet on it though, people have survived falling from an airplane without a parachute, but generally, they don't.

PeterL
09-07-2010, 10:25 PM
Without stretching imaginations at all you could have a sword made of high quality stainless steel that was well sharpened. A two handed sword of that sort could easily remove a head, and it could cut an ordinary sized person in half at the wais, some of the time. Remember that kukris have been used for beheadings, as were two handed swords, and they were carbon steel. A few feet of sharp steel swung by someone with training can cut very well.

efreysson
09-08-2010, 02:00 AM
In principle, yes.
Keep in mind though that action=reaction always applies. Swinging around a sword weighing half a ton will likely result in the character getting stuck knee deep in any ground that's not solid rock. Hitting something would not send them flying (since most of the force comes from the sword's impulse) but forcefully swinging the sword might. If the sword's around a hundred kg, that means any movement would result in the wielder being accelerated about as much as the sword (same force since action=reaction, and same acceleration since a=f/m). Being superhumanly strong doesn't make your feet stick to the ground better than a normal persons.

Hmm. I have toyed with the idea of making the super-warriors themselves ultra-dense and heavy. Would that make a difference? Or if the sword was heavy but not THAT heavy? Maybe 50 kilos or so?

Lhun
09-08-2010, 07:02 PM
Hmm. I have toyed with the idea of making the super-warriors themselves ultra-dense and heavy. Would that make a difference? Or if the sword was heavy but not THAT heavy? Maybe 50 kilos or so?Well, action=reaction. You can easily do the calculations (or an estimate) in your head for any specific case. The sword and the wielder experience the same amount of force accelerating them (in opposite directions) if the sword gets swung around. So if the sword is half as heavy as the wielder, he gets flung around half as fast.
Having the warrior be heavier of course allows for a heavier sword, but then you have to keep in mind the usual weight problems. Wooden staircases probably won't break, unless he weighs hundreds of kg, but just think of the many situations where even differences between the weight of a big or small but normal human matter, such as walking on a frozen lake, crossing a swamp, climbing a tree or just walking around on a beach (you're not going to disappear in the sand, but even sinking in a little bit farther makes walking/running much harder). Sinking in isn't the only problem, friction is another. Being heavy does increase this somewhat, but if you're as heavy as a car, you'll need as long as a car to come to a full stop or accelerate. (more even, since 4 wheels give better friction on the ground than 2 feet).

Kenn
09-08-2010, 08:00 PM
I am disappointed in you Lhun;)

kg are not units of weight. Why should four wheels provide a higher level of friction than two feet (think about the second law of friction). Finally, the sword and the wielder do not experience opposite forces unless they fly apart.

Lhun
09-09-2010, 01:34 AM
kg are not units of weight.Weight or mass, doesn't really matter when in a static gravity field. ;)

Why should four wheels provide a higher level of friction than two feet (think about the second law of friction).It's all about the rolling resistance. ;)
Edit: and also about the ground conditions. On an idealized infinitely sturdy ground the surface area is indeed not important to total friction, but on normal ground, there's a maximum friction per square inch you can get before the force breaks apart the material. (Which can be very little if the material is loose sand or soil)

Finally, the sword and the wielder do not experience opposite forces unless they fly apart.If the wielder yanks on the sword, he does. I was talking about accelerating the sword, not about the sword impacting something.

Kenn
09-09-2010, 01:58 PM
Weight or mass, doesn't really matter when in a static gravity field.
It does if you re a physicist. Your statement is also incorrect, because it neglects buoyancy effects.

It's all about the rolling resistance.
Edit: and also about the ground conditions. On an idealized infinitely sturdy ground the surface area is indeed not important to total friction, but on normal ground, there's a maximum friction per square inch you can get before the force breaks apart the material. (Which can be very little if the material is loose sand or soil)
Rolling resistance is something entirely different. It is the drag on a rolling body.

If the wielder yanks on the sword, he does. I was talking about accelerating the sword, not about the sword impacting something.
It's all about turning moments and the frictional reaction at his feet.

Get out of that one Lhun;)

Lhun
09-09-2010, 04:10 PM
It does if you re a physicist.I'm not a physicist, i don't care about being exact beyond practical requirements. :p

Rolling resistance is something entirely different. It is the drag on a rolling body.Yes, and it's generally higher than dry kinetic friction.

It's all about turning moments and the frictional reaction at his feet.Only as long as you don't scale up the forces involved beyond the limits for normal ground material (and shoes).

Kenn
09-09-2010, 08:37 PM
I am; no, it's not; and I don't know what you mean.

The first is not being pedantic, as it can mean whether you sink or float.