Foot-pounds of a good punch?

[PaladinX13]

I'm just curious about the "energy" of a good punch... I'm not terribly interested in discussion about placement or transfer just the physics.

[Jody Hudson]

Mass X Speed X Speed or MxVsquared.

The idea, as explained to me, is to put a good deal of body mass behind a very fast punch and to aim at a point behind what you intend to hit, whether with a punch, kick or weapon.

I'll hypothicate here just for grins. If I put 150 pounds of my 250 total weight into a 70 mph punch or kick...

That would be... 150 X 102 feet per second = 15,300 foot pounds of energy IF I did it correctly. Of course then there is another factor and that is the foot pounds of force per area of application. Let's say that is a flat fist punch and the contact area is 7 sq. inches. 2,185 pounds per square inch...

Now... I conjecture that I messed up here at least seven or eight places in assumptions and calculations.

Now let those who can really figure it out -- correct me, so that we can all learn.

[LawDog]

Hmm.

I know that a precordial thump, which can sorta be described as a half-power hammer fist to the chest, delivers ~5 joules of energy.


According to this nifty little converter:
http://www.engnetglobal.com/tips/convert.asp?catid=12
five joules is about 3.69 foot-pounds.

LawDog

[PaladinX13]

Hard to imagine something like the above being of such little magnitude! Hell, I've got some airguns that produce greater ft-lbs! Thanks for the info.

[Dave R]

I think both calculations are off by an order of magnitude or so. Jody, maybe your mistake came in coverting FPS to foot pounds??

Just thinking practically here...a foot pound in the amount of energy needed to move one pound one foot.

In the boxing photo, if 100% of the punch's energy were transferred to the target, and if the target were rigid, it looks to me like it would move the body 1-2 feet. Assuming the body weighs 250 lbs, that's 250-500 ft. pounds.

Another way to look at it...if I move my entire body one foot in generating the enrgy for the punch, I have theoretically created my body weight in ft. pounds. With good technique and velocity, could I double my body weight in ft pounds? Maybe.

So I think the truth is going be somewhere around 1/2 body weight to twice body weight in ft. pounds.

Who needs math when you can BS like that?

[Jody Hudson]

Well, I suspect that my calculations are in fact incorrect but have no clue where. The important thing to remember however... is that it is Mass once TIMES VELOCITY SQUARED. Thus speed is factored in doubly as much as mass.

That is why the most powerful punchers and kickers work on FAST TWITCH muscles to get the punch and kick faster and faster AND why the little fast guy can sometimes SMASH the big slow guy beyond all expectations.

[shucks]

they said that something like 200 ft lbs was necessary to break a brick with a knife hand strike,and that the most powerful such strike ever measured was something like 250 ft lbs. The knife hand has CONSIDERABLY more power than the punch. Most people's punch will be little more than 100 ft lbs, at best, and most of it will be wasted by improper focus, accuracy,target choice, angle of deflection, allowing the target to "yield" with the blow, etc. That is why FEW people can fight effectively with their hands.

[Azrael256]

I don't know about you guys, but my fist doesn't move at a constant speed when I throw a punch. My fist tends to accelerate until I extend to the end of my reach, so I try to place the person I'm punching just inside the end of my reach so that I can get the maximum effect. The formula here is F=ma, not mv^2. From that you can calculate the exact energy.
The boxing photo is pretty cool, but it is in no way an accurate measurement. Not only is the neck flexible, thus removing the vast majority of the mass of the poor schmuck getting punched from the equation, but we are also dealing with an angular velocity calculation because no matter how hard you punch the guy, he doesn't fly straight back.
Probably the best way to calculate this would be to punch something of a known mass and see how far/fast it moves. That is why we use those punching bag type devices you've probably seen at bars and such.

[C.R.Sam]

And remember to do it without a glove on. Gloves absorb a lot of energy. Boxing gloves absorb energy while spreading the blow over a wider area. Of course the breaking of knuckles, finger bones and wrist bones absorb energy too.

Ahhhh, forget it.

Have seen results of bare handed punch where orbital process of skull was fractured. Recipient dead.

Sam

[Dave R]

Wow. A one-punch stop.

[Jayman]

I don't know about ft/lbs, but I saw some old karate (ISKA, or something, I forget) matches, and before the matches, the contenders would throw techniques into this heavy bag with a meter on it to measure PSI. The really good/hard punches and kicks were around 2,000 PSI, which is a serious amount of ouch.

That said, these guys were pros, and they could hit like MFers, obviously. I don't know if they could hit quite as hard as some of the heavyweight pro boxers, but probably close.

[Skorzeny]

Much like handguns, an effective punch (or a kick) has a lot more to do with placement than necessarily the force or kinetic energy with which it is delivered.

That is not to say that force or KE has no meaning, but rather that the factor of placement has a great coefficient, if you will...

Skorzeny

[ICBentley]

I would figure the force of a punch (not energy) not by what you put into it, but by what is taken out by the strike (i.e. what is actually delivered). With your best blow (assuming your hand is perfectly elastic (i.e. all the force is delivered none dissipated in your hand) how fast can you make a 1Kg (perfectly elastic, stationary) mass go in a frictionless environment devoid of other factors. This would be difficult to estimate. It is even more difficult to decide what, if anything, it means.

However, impact (or impulse = force X time) and the area over which it is spread are more important than energy or force alone, though related. The impact applied to the tissues struck and the vulnerability of those tissues to that impact seem to be important factors in strike efficacy.

I participated in a physics of martial arts email list for a time. I quit when it became apparent that: the physical quantities involved are very difficult to measure, the physical systems involved are exceedingly complex, too many assumptions were needed to reach any difinitive appearing answers, physiology and psychology are too important for physics alone to yeild answers a fighter can actually use.

For example all of these may stop a fight in one blow: high force blow to the correct part of the head (you want high leverage against limited muscular strength), moderate force blow to the nose causing reflex eye closure, mild to moderate force blow in the right direction to the knee, low to moderate force to the proper areas of the throat. One could go on, but the point is that the art of getting the right blow to the right target at the right time is what is useful.

Overgeneralizing to emphasize the point, Boxing is an art which involves high force blows to limited targets, Taiji (as a fighting art) involves multiple lower force blows to a higher number of highly selected targets of physiologic import. Both work. The art is more important than the physics as each was developed by experiment in the real world which involves systems of such high complexity that they defy rigorous analysis (too many variables).

Learn your art. When martial artists talk about science they are often full of bulltwinkies. When good martial artists talk of fighting they more often know whereof they speak.

Bentley

"There is more truth in one sword than in 10,000 words.."
-The Koran