Tuesday, January 02, 2007

How hard can human muscles strike with a sword?

One interesting data point is a survey carried out within the Society for Creative Anachronism.

If you're familiar with armored combat within the Society, skip this paragraph. The Society, or SCA uses weapons made of rattan and other materials that approximate the weight and balance of medieval weapons. The goal in armored combat is to strike a "good blow", one assumed to hit hard enough to be effective against medieval armor of a particular period. Lighter blows than this standard are ignored.

This article describes a survey carried out some years back to attempt an objective quantification of this subjective standard by smacking a bowling ball off a post and measuring how far it flew before hitting the ground. It should be possible to calculate the number of Joules transmitted to the target. Unfortunately, the calculations are trickier than I originally thought, and for now I will simply direct you to the first comment below, which responded to an earlier draft. These estimates seem to assume a single handed sword, and a significant number of people can hit harder than the upper end of the range if they want to: the Society frowns upon hitting harder than necessary for safety reasons.

It's also important to remember that many blows in combat land with less than the optimal amount of force the striker could deliver, typically because the target moves in a way that makes the biomechanics less than ideal.

1 comment:

Anonymous said...

Hello Will,
I took the time to go through the values concerning bowling balls and impact in the linked article (I’ve been looking for that link. Thanks). I believe that you may have both an error in your calculations and an error in your assumptions.

After converting everything to metric and looking at KINETIC ENERGY:
A bowling ball struck lightly will have a KE between 3.166 and 6.689 Joules. Avg 4.688 and a std dev 1.181.
A bowling ball struck moderately will have a KE between 7.661 and 15.708 Joules. Avg 10.978 and a std dev 2.813.
A bowling ball struck strongly will have a KE between 13.831 and 28.626 Joules. Avg 20.018 and a std dev 5.137.

In all cases the lightest balls had the highest kinetic energy.

If we look at the MOMENTUM however:
A bowling ball struck lightly will have a KE between 3.390 and 3.542 Joules. Avg 3.469 and a std dev 0.042.
A bowling ball struck moderately will have a KE between 5.268 and 5.367 Joules. Avg 5.305 and a std dev 0.033.
A bowling ball struck strongly will have a KE between 7.084 and 7.233 Joules. Avg 7.164 and a std dev 0.044.

There is no consistence of which balls or which heights had the greatest or least momentum. Given the accuracy of the measured data (tape-measure, mark in the sand, verticality of the pole, etc.) the momentum values are wonderfully consistent and a perfect school example of the conservation of momentum principle (which most collisions are).
Without knowing the mass of the impacting weapons and its resulting velocity after impact it is impossible to calculate its original velocity. Without the mass and velocity of the original weapon we can not calculate its original kinetic energy.
While we could measure a collective sample of weapon weights and then assume that the rattan sword followed the bowling ball in a non-elastic collision, without knowing the flexibility of the rattan it becomes impossible to calculate the peak impulse that would be useful for calculation of penetration capability.

I think that we need to approach this from a different set of calculations.