Blade shapes and their uses

I've always wondered: why are swords with curves (such as katanas, samshirs, etc.) considered to be, all other things equal, superior cutting swords? What about the curve makes them cut better?

Also, what about swords with inward cutting blades, such as the yataghan? Are these sword blades better at cutting than straight (or even type XV-type XVIII) bladed swords?

The curve would facilitate slicing more than a straight blade.

Llew2 said:

The curve would facilitate slicing more than a straight blade.

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At the loss of some of the intuitive stabbing* ability and versatility of straight, double-edged swords.

Stabbing with a curved sword is very much possible, but it takes more technique.

by the way that link is broken

Llew2 said:

The curve would facilitate slicing more than a straight blade.

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But my question is, why?

Think about it

Take a knife or similar flat bladed object and a loaf of bread or similar cuttable object. Cut the bread as you normally would, but pay particular attention as to what happens to the tip of the knife as you do.

Well, the tip simply sinks into the material along with the rest of the blade, as expected...

It's all about contact area. A curved blade swung at the same speed as a straight blade of equal mass would exert the same amount of force on a smaller area because it has less contact area. This concentrated force on the curvature cuts better than distributed over a long straight edge. It's the same reason why lying on a single nail will give you a puncture wound but lying on a bed of nails is possible without hurting oneself (if done properly).

allthesedamnnamesaretaken said:

It's all about contact area. A curved blade swung at the same speed as a straight blade of equal mass would exert the same amount of force on a smaller area because it has less contact area. This concentrated force on the curvature cuts better than distributed over a long straight edge. It's the same reason why lying on a single nail will give you a puncture wound but lying on a bed of nails is possible without hurting oneself (if done properly).

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Alright, but on a sword, does that give diminishing returns? Ex: some samshirs have very deep, almost quarter-circle curves. Does this make them that much better at cutting than a katana, which has less of a curve?

Precisely. A curved blade on the other hand will slide rather than sink. This gives you a much better cutting angle, since you're usually hitting at 45 rather than 90 degrees to the target, plus you effectively have a point to hit with which makes it more accurate on the swing than a straight edged sword.

This gives you two advantages. The first is particularly apt for cavalry and heavier examples - there's less risk of the blade becoming 'stuck' in an opponent and being levered out of your grasp. If you imagine a cavalryman swinging his sabre at an infantryman as he passes, there's a good chance a flat blade will be jolted out of your hand. A curved blade on the other hand will naturally slide across the target.
The second is the nature of the damage caused. A straight sword results in a 'hack cut', i.e. it bites in and is then usually withdrawn. A curved sword on the other hand can be used for "draw cuts", i.e. you can slide the sword across the opponent, causing a much longer (although possibly shallower) wound. It's possible that the heavier examples were an attempt to give the wounds greater depth. Either way, an unarmoured opponent is likely to be incapacitated in a single swing, and probably bleeding to death if he's not already trying to put his entrails back in.

One of our resident swordsmen could probably put it in more technical terms, but that's roughly the physics behind it.

Too much to go into.
Just look here:

http://forums.swordforum.com/showthread.php?t=49143&highlight=curved+blade

http://forums.swordforum.com/showthread.php?s=&threadid=3864

With weapons like the yataghan, Gurkha kukri and Ancient Greek Kopis most of the weight is at the tip of the blade, so when you do chop or hack you get much deeper cuts.

Naridill said:

The kukri, despite the size, can take a man's head off in a single blow.

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So can a carving knife. So can just about anything, if done right.

Archonsod said:

A curved sword on the other hand can be used for "draw cuts", i.e. you can slide the sword across the opponent, causing a much longer (although possibly shallower) wound.

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This is not exclusive to curved blades, it is simply more efficient with them. German and Italian longsword techniques contain what could be termed draw cuts, as well as rapier.

Naridill said:

Well, of course, but a carving knife wasn't designed for decapitation, was it?

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Mine are. But the curved blade also helped not getting your blade stuck due to the roundish shape.