Curiosity Question.

David Stifle

David Stifle

Joined
Nov 20, 2008
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Which sword will bite the deepest, a light very fast sword, or one with more mass behind it? Does speed equal impact, or does weight equal impact? I suspect the heavier sword would, yet when I think of a blade being swung much faster than the heavier one, I end up needing a drink.:) Can anyone help me out here?
 
I think they both have similar potential, but probably need a bit different blade geometry to be optimized, and a bit of difference in technique when used.
 
I've mentioned Vincent Chevalier in the past

http://blog.subcaelo.net/ensis/cutting-mechanics-hints-sources/
http://www.thearma.org/forum/viewtopic.php?t=24138#.VZiIPnqUzGc

Here are Tinker's thoughts
http://www.swordforum.com/forums/sh...ting-power-cutting-ability-in-swords-a-Primer

An older Arma article
http://www.thearma.org/spotlight/GTA/motions_and_impacts3.htm#.VZiJOHqUzGc

More theory
http://l-clausewitz.livejournal.com/273098.html

Can a heavier blade at a slower speed equal the cutting power of a lighter sword at a greater speed?

Yes, and vice versa.

What are we cutting? What is the motion? What is the length? What is the force? What is the weight? What is the cross section? How sharp is it?

The variables are more numerous than any choice of favorite beverage. There are numerous attempts to put blade dynamics into a single formula but none I have seen account for all variables. I am no Sheldon Cooper but there may be a physicist out there willing to postulate one.

What is the perfect sword?

Cheers

GC
 
The formula for kinetic energy is M X V² where M = mass and V² = velocity squared.

Everything else being equal, increasing speed pays better than increasing mass.

Of course, nothing is ever equal.

You won’t cut through a hauberk with a small sword.
 
Wow! There is some very heavy thought behind my not so simple question. I guess I should have realized, certainly the variables are vast and definitely hard to demonstrate in action. In any case, since I am making a light, very fast sword I shall have the opportunity to test it out to some extent.
 
I think that regardless of weight, a thin sword bites the deepest, as long as the metal can support the cutting edge without buckling.

Even a heavier sword feels more light and quick if it's balanced out well with the hilt and a big pommel. Speed is a top-level trait in a weapon, desired even if it means more weight!
 
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Swords and bullets. the argument continues. Faster and lighter or slower and heavier.

I don't think its possible to have the perfect sword unless you know exactly what you'll be trying to cut into. Its like having one golf club for everything.
 
Mecha said:
I think that regardless of weight, a thin sword bites the deepest, as long as the metal can support the cutting edge without buckling.

Even a heavier sword feels more light and quick if it's balanced out well with the hilt and a big pommel. Speed is a top-level trait in a weapon, desired even if it means more weight!
Click to expand...

I think Mecha is right, edge geometry blade shape, and overall blade thickness will play the largest role in how deep a sword bites. With that aside, kinetic energy, ((1/2)mv^2) plays another significant role.

So I guess your answer depends on how much faster the smaller sword is swung that the heavier sword.
 
Schmoopy said:
So I guess your answer depends on how much faster the smaller sword is swung that the heavier sword.
Click to expand...

If both swords were swung with equal force, would the tip of the faster, lighter sword travel faster than the tip of the heavier blade? I know, variables. For me, it's just fun to ponder these things.
 
F=MA would seem to apply here. So would momentum, as well as the aforementioned kinetic energy. A lighter sword will be quicker to accelerate to top speed, but you're ultimately limited by how fast you can swing your arm, so I'd guess that, up to a certain point, heavier blades can theoretically move just as fast as lighter ones, given sufficient space to accelerate. A heavier blade is also harder to stop, which can be a good thing and a bad thing. When you hit something, you get a transfer of kinetic energy and the normal force and force of friction working to slow the mass of the blade down. More mass means it's going to cut deeper on its own, all things being equal, than a lighter sword moving at the same velocity. But it's much more complicated than even that. You also need to take into account the geometry of the cut. Is it going to work like a draw cut, as in the case of a katana, where you have slicing happening along with the chopping? Or are you just putting edge against whatever it is that your cutting, and relying on speed and mass of the blade to generate your cutting? And that's leaving aside the variables already mentioned.

Too, do you have to contend with armor, or not? How tough does the blade need to be? Modern opponents are either going to be trees/pool noodles/tatami/water bottles, etc, or else people who are all too likely unarmored. I'd tend to prefer a lighter, faster blade (or two) against all but the trees, and I don't plan on cutting down any trees with swords anyways, so it's a moot point in my case.

To answer your most recent question, it's less IMO about the sword and more about the wielder and how fast they can move their hands. I can cut just as quickly with a well-balanced 5 pound sword as I can with a well-balanced 2.5 pound sword. 5 pounds is about my limit for speed. In all cases, that upper limit of force generated, and the amount of space we have to make the cut will determine the possible acceleration and thus, highest velocity, that can be generated for whatever type of sword.
 
One thing about a light-weight sword is that you can gain quickness from wrist articulation.
 
Realistically too it is who is using the sword. A good understanding of body mechanics and the swords limitations/abilities will yield the most effective result. Give a samurai a bastard sword and a medieval british soldier a katana, likely they would not be as efficient with the new weapon as compared to their own regardless of the weapons shape, size and mass. No simple answer for this question lol.

Happy hunting!
 
Lightsaber :D
No? lol. ok.
Too light means not enough penetration..
Too heavy means unwieldy..hard to recover
Medium..like a longsword, or one hander. there's probably a reason those saw so much use.
As to "bite"..I'm not sure a human being could generate the required speeds to match the bite of a heavy sword with something like a small sword, or rapier,etc. A gladius could certainly wound by cutting, but it lacked in that as opposed to say, a grosse messer. That's why the point. in my observation, generally shorter/lighter means "more stabby", like the rondel dagger, gladius,small sword, etc, but not always.
 
Ok, keeping it to mass and acceleration, Force = Mass x Acceleration (or Velocity squared). Inertia (in simplified form, the inertia of a rod rotating around an axis at the end of its Length) is (Mass x Length squared)/3.

So, the more mass and/or length, the more inertia you have. High inertia is good on the cutting end, less so when you're starting the swing. Excessive mass or length means that you are going to have a hard time overcoming the inertia to get the blade moving, and your acceleration is going to suffer. Lots of mass with little acceleration is still going to equal a small amount of force.

In the F=mA, it's easier to up the A and keep the m low. If there's too little mass, though, it will not have sufficient inertia to bite in deep, and your penetration will still be shallow.

So, in my opinion, you need the blade light enough to move easily so you can get fast acceleration, but with enough mass to it that it will have sufficient inertia to bite deep on impact.

If you're looking more at point work and stabbing, speed to overcome your opponent's bladework becomes more important, and the weight to chop becomes weight that slows down your point.

I never was good at math, though. :D Momentum, kinetic energy, and I'm sure other physics is involved. It's those darn Newtonian Laws of Motion.
 
When the Society for Creative Anachronism began, nobody had a clue how to use medieval weapons. Sword and shield fighters copied their “On guard” stance from manuscript illuminations and tapestries. They showed the shield in front. Knight hiding behind it. His sword held above his head, parallel to the shield. For years that was the standard sword and shield stance.

Then Darwin stepped it. Brandishing your weapon above your head might look heroic. But it telegraphed your every move. Something else worked better, and won tournaments: Shield in front. Your sword hand just above your shoulder. Your blade hangs down your back. This has several advantages. Start your cut as though you were a boxer jabbing. Your hand and sword can be well in motion, building kinetic energy, before your foe has a visual clue. The same starting position lets you strike from straight down to a sideways body blow to a leg cut. All of them look the same when the move begins. Starting behind you, the blade has a clear swing that gains maximum speed by the time you strike. Delivery is with a snap cut that adds angular momentum to the mix.

This is one example. About one class of blade. From one martial system. Such factors matter in the real world.

There are more things in swashing your buckler than are dreamed of in your equations, David.
 
I think the question is finding the correct sword for a person.

Angular momentum, moment of inertia, and center of percussion dictate impact strength; not kinetic energy. And blade shape and handle length is at least as important.

Back to my first statement your arms becomes part of the arm-sword system in calculating angular momentum through moment of inertia.
 
gregorio said:
I think the question is finding the correct sword for a person.

Angular momentum, moment of inertia, and center of percussion dictate impact strength; not kinetic energy. And blade shape and handle length is at least as important.

Back to my first statement your arms becomes part of the arm-sword system in calculating angular momentum through moment of inertia.
Click to expand...

Could you elaborate further?
I understand these are all factors, but wouldn't blade shape (IE edge geometry) still constitute a significant variable in how deep a blade sinks into the target, because a narrower grind with a curvier blade would reduce the contact area for a more effective cut?

Also, wouldn't a longer handle allow you to build both greater inertia and momentum, since the length would increase the velocity of the blade end?

Regarding the center of where translational and rotational forces cancel out, isn't this a non factor since you can just strike with contact at the next node when the weapon is longer, or widen the blade to move the node to next location?



Regarding the ideal mass, it would be an amount of weight which when you swing, accelerates to the maximum biomechanically limited speed at which you could swing your empty arms, immediately before the blade contacts the target.
 
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