# Geting the mass of a karate punch.

1. Oct 11, 2007

### LuckyCharms145

Hello I've been looking all over the internet for the answer to this but cant find it. I saw some wires that you hook up to anything and it measures the mass but how can i do something that wont cost me 300 dollars? A quick easy thought was to get a weighing scale and punch it but I just doubt it, besides my scale is dirty and I dare not hit that thing lol. I don't know if this helps but its for a science project that I am doing, my question is at what velocity & mass can my punch stop a human heart.

2. Oct 11, 2007

### vanesch

Staff Emeritus
The "mass" of a karate punch doesn't make sense. Mass is a unit of matter. Probably you mean the amount of momentum that you transfer to the target with a punch. The simplest way I can think of is a "ballistic" measurement, which is the technique that is used to know the impulse transfer of a bullet hitting its target. You essentially hang up a kind of punch ball to the ceiling and when it hangs still, you hit it, and try to determine the amplitude of the swing (for instance, the angle the rope maximally makes with the vertical line). From the length of the rope and the weight of the punchball, one can calculate the transferred momentum in the punch.

3. Oct 11, 2007

### Loren Booda

There will probably be an optimum weight for the "ballistic bag," as well as an optimum depth at which to strike it. You could measure the angle of the bag's displacement over a reasonable number of tries to find a likely maximum force (throwing out any skewed results). Even a comparatively small impulse can register as a large one, or vice versa, if you are not consistent with your punches.

You may want to look up "cardiac plexus."