Musings on Fighting and Physics

“	Originally Posted By: PlumDragon I think there is a general misunderstanding here in the basic physics of collisions. Acceleration, and jerk (the derivative of acceleration), are very important for an object to build up to maximum striking power. But it means very little in terms of transferrance of force in a collision--what it does do is allow you to keep putting in some effort in post-collision in order to reduce the rate of deceleration and "hit through". Nevertheless, the goal should be to acheive maximum velocity prior to actual impact. See post #11 of this thread. And of course, none of this makes much difference at all to real life after reading Post #16...	”

Plum, I feel looking at only initial velocity (Vi), without continued applied force at contact is the wrong way to go - i.e. this generates very little striking power, unless v is very large, or again unless mass is large.

Here's why - looking at basic collisions and assuming no distortion of the objects involved (face, fist, etc) then any and all force/energy transferred is subject to conservation of momentum m1v1=m2v2

...or in this case assuming a fist (M1) travelling at an initial constant velocity (V1i) hitting a static head (M2):

M1(V1i) = M1(V1f) + M2(V2f)

Working backwards, the only force transferred can be inferred from taking M2(V2f), and calculating its acceleration based on its final velocity (V2f) (starting at V2i=0 of course)....



Let's take this to an overly simplistic simplification... you guys have all bought meat at a butcher's before, right? How much do you think a typical fist weighs? a pound? maybe 2 at the most? let's say the weight of a shoe or at most a hiking boot.

Scenario 1: initial velocity with no applied force
Now because it's essentially the same motion, the maximum speed you can give to a punch is roughly the same as you can get by throwing that shoe (give or take a tiny bit for the extra weight of the shoe, but most likely negated by the difference in mechanics of an overhand throw accelerated around a couple extra levers vs. a punch) .

Now take a heavy bag - I challenge you to throw that shoe or boot at the bag all day and see if it buckles or budges.

This scenario is the equivalent of looking only at initial velocity (Vi), without the use of applied force (or jerk if you want to go further, which would be even better).

Scenario 2: applied force without or without initial velocity
Continuing on with the example above, grab that shoe or boot and put your fist through it... Now whack the bag - punch it like you've always done.

So... which do you think is more effective? Why?

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What is the sound of one hand clawing? -- chanh buddhist proverb

I think youre analyzing the problem wrong, Mok and I think your 2 scenarios are flawed inthat you are measuring the wrong variable change.

First off, I covered the issue of "hitting through" above in my post. I said, quite specfiically, that it is relevant, as is a number of other things, even things like friction if we want to talk about higher order effects; its just not as much as everyone seems to think it is. The acceleration and jerk is highly important in getting the hand up to speed, in developing the power...NOT in transferring it.

Second, your examples fail to take into account the employment of mass. You can push a heavy bag all day long by emplying force and causing an acceleration, but it isnt going to cause any damage. Its the velocity on impact (coupled, obviously, with the mass, and a number of other variables) that causes the damage due to a high difference in kinetic energies. I did too many labs and studies and tests on this as a Physics undergrad to believe anything different, until I can see a matlab model or something show otherwise.

I wish I could type more but I am in quite a rush to get out some afternoon orders... =)

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PlumDragon Herbs: Dit Da Jow and Iron Palm Liniments

"When a handshake passes the elbow, it becomes Judo."

Plum,

I think you're right about K.E. (as pointed out largely dependant on speed) being the dominant factor for damage done, but it's not the only factor.

Your analagy about pushing a bag is a very good one, but nevertheless we can't ignore force altogether. We know the body (like all materials) has force limitations - e.g.: it takes "x" pounds/square inch to puncture skin, "y" to crack a rib, "z" to break a femur, etc. A couple examples: when the "Fight Science" show was calculating its impact ratings, or when MythBusters puts their dummy through collisions - they always use force as the scale. So Newtons, kiloNewtons, pounds/square inch, whaichever - force is always a factor. Maybe it's because force is much more readily measured then energy (?), but nevertheless it supports force being a relevant scale.

That said, I want to go back to my initial post about about speed having a very quick cutoff (how fast it is humanly possible to punch), and maximizing both speed, mass, and force.

The reason for why my shoe analogy is flawed is that in a normal punch the fist is not a disconnected mass and isn't being tossed at a target like a shoe. Problem is some people really do punch like that or imagine that speed without structure will somehow make you a killer striker. This is the point Cam made, and one which I completely agree with.

Now given that the max speed of the fist is relatively constant, what makes a more effective punch vs. a weaker one? Why do some people, punching approx at the same speed as another, deliver far less impact? The answer is "connectedness", i.e.: structure.

By "punching with the core", what is really meant is supporting that punch so that in effect it has more of the body's mass behind it. The thing is that structure requires strength (force) to support it. The human body being what it is, you can't project momentum or force from hips to knees to shoulder to elbow to wrist and finally to fist without some kind of tensile strength holding your skeletal system together and preventing it from collapsing on impact.

Even if you're doing swinging strikes like hooks, tensile strength is still an issue. So to take the "ball on the end of chain" analogy, in the case the arm acts like a chain and generates the centripetal force needed to swing the weight in motion, and keep it together on contact. The heavier the ball and faster the orbit, the stronger must the chain be. And believe me if you're going to be swinging hooks or haymakers like you want to tear someone's head off, there's considerable strength that is needed pulling the arm in and keeping it together on impact... And as soon as you slack off on the pulling (on impact), even if you keep speed same, the structure collapses, force and mass is not transferred (and hence less energy), and your "strike" will bounce off the target (likely jarring your arm little) rather than delivering that satisfying impact we're all looking for.

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What is the sound of one hand clawing? -- chanh buddhist proverb

Great post, man!

A couple quick things to still clear up:

- I agree K.E. is not the only factor. In fact, if youll go back to some of my previous posts I try to say a number of times that there are LOTS of factors involved in this type of problem. It wouldnt surprise me if when calculating things in a complex model that there are 40 or 50 or 60 variables that need to be accounted for. 7-level models routinely have that many variables or more. That being said K.E. is probably the most important 1st order factor.

- The reason force is measured on impact in the show or on Myth Busters is the acceleration of the bag from rest. On a collision, the energy is transferred to the other object as a force. Its the force that is measured by a machine, but energy (in this case, final velocity, among other things) that allows the force to be exerted. The hand decelerates because of the bag, and the bag accelerates because of the hand. In a lossless world, the sum force that the body put into the punch would be the exact force measured against the bag. , assuming a couple of benign things not worth discussing. Of course, we havent even talked about pressure yet!! =)

- I couldnt agree more, its all about proper structure and bio-mechanics. Naturally every system does it a bit differently, but striking with proper structure is the best way to build up additive force at different joints, etc. Earlier there was talk about f=ma....This is perhaps the most trivial and useless form of the equation. Taking it one step forward would put sigma signs on the front of the equation and (ma)1 + (ma)2 + ... + (ma)n on the other side. Every time we get to a joint or a fulcrum with some moment, thats one of those ma pieces.

In the end, its all for discussion. As I had said in previous posts, our brain takes care of the optimization process subconsciously as logn as we practice properly with the proper focuses. Instead of solving an equation or realizing its energy vs force, or why elasticity is important, or even friction, or pressure, our brain goes through a very intricate weighting process that solves the problem real time in tens of thousands, or more, repititions and an understanding of physics becomes irrelevant in manifesting our endeavors in reality. But its sure fun to talk about!!

EDIT: I just realized you mentioned tensile strength. Tensile strength generaly refers to a compression and not an expansions. Nevertheless, Id be willing to bet both are variables in a really high order model, as well as RATE of compression/expansion...that is actually a VERY important thing to know. But for the sake of this discussion, its probably well beyond diminishing returns to worry much about it in this context, as the math can get crazy in a hurry; it would be safe to consider for now that the body can handle the pressures generated due to proper pre-conditinoing as well as the rate of these compressions and expansions.

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PlumDragon Herbs: Dit Da Jow and Iron Palm Liniments

"When a handshake passes the elbow, it becomes Judo."

“	Originally Posted By: Lugaldamhara Let's not confuse speed with acceleration. Many point fighters can deliver the fastest strikes imaginable but they don't have the power to bust a grape simply because the acceleration is generated from the limb and not from the core. Proper technique means greater acceleration, and can still be great in quantity with less speed. Boxers are without a doubt the most powerful punchers, and Muay Thai fighters are also, without a doubt, the most powerful kickers. This is based on their technique and core generation of acceleration. Speed without acceleration does not equal power. Peace- Cam	”

SORRY I DON'T MEAN TO BE RUDE BUT WHAT YOU ARE SAYING DOESN'T REALLY MAKE SENSE. ACCELERATION IS SIMPLY CHANGE IN SPEED OVER TIME. SO IT HAS NO RELATION WITH REGARD TO WHETHER IT COME FROM THE CORE ON NOT. THE ONLY WAY TO GAIN GREATER ACCELERATION WITH LESS SPEED IT TO DO IT OVER A SHORTER PERIOD OF TIME

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Senior Instructor
Geoff Bennett Martial Arts International
Progressive Protection Systems
www.martialarts-int.com

Dude - is your beer stuck on capslock?

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What is the sound of one hand clawing? -- chanh buddhist proverb

“	SORRY I DON'T MEAN TO BE RUDE BUT WHAT YOU ARE SAYING DOESN'T REALLY MAKE SENSE.	”

Because something doesn't make sense to you it doesn't mean you are being rude.

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Rock On!
Cam
"Raise up your mind....."

All the physics brought up so far seems to be assuming single vectors, no?

Talk of structures etc implies multiple vectors are in force.

It should be possible to model them without too much complexity (?)

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Consider Phlebas, who was once handsome and tall as you
High mountains are a feeling
I don't need to sell my soul, he's already in me

“	Originally Posted By: john100 All the physics brought up so far seems to be assuming single vectors, no? Talk of structures etc implies multiple vectors are in force.	”

No, on 2 accounts:
1. There was specific talk of multiple vectors; I even expanded the worthelss f=ma equation for use with multpiple additive vectors. Whic brings us to...
2. In Physics, there are vector components, generally in a 3-dimensional space. A magnitude in each direction. Those vectors are "added" through a mathematical process to give one single vector that equally signifies a magnitude and direction of all the vector components...

This is exactly why the topic is so difficult to discuss without having a decent background in Physics.

“	Originally Posted By: john100 It should be possible to model them without too much complexity (?)	”

Depends on what you mean by "model". If all you want is a basic undamped collision of two spherical objects at some given relative velocity, with no elasticity, no friction, no moments of inertia around things like joints, no contunial addition of energy at the time of impact, no worries about stabilization (rooting...or floating in the case of a boxer), etc etc etc etc...Then sure, Id bet you can find a little java applet floating around on the web somewhere...

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PlumDragon Herbs: Dit Da Jow and Iron Palm Liniments

"When a handshake passes the elbow, it becomes Judo."

“	There was specific talk of multiple vectors	”

oops, sorry, missed it

“	to give one single vector that equally signifies a magnitude and direction of all the vector components	”

it's coming back... but from working with this stuff (though with much bigger numbers ) massive approximations are pretty much normal... to the point I carried all components through for each calculation.

“	If all you want is a basic undamped collision	”

I was thinking some approximations could be built using fluid dynamics - they use it for all sorts of stuff from steel milling to smoke dispersion without allowing for specific conditions. I'm not volunteering though.

__________________
Consider Phlebas, who was once handsome and tall as you
High mountains are a feeling
I don't need to sell my soul, he's already in me

lol, neither am I!! =)

Its possible you could find a simulink model out there for a really specific application. It could offer an interesting academic look, and perhaps with minial modification could symbolize some type of collision liek what were talking about...

What would be really cool is a good model/sim that takes into account all the joints in the human body and has weights for each of the muscle groups...From there we could start to really understand power and speed production, showing how each moment adds to overall energy output. Unfortunately, thats a massive undertaking that a whole team of engineers would have to tackle...

“	it's coming back... but from working with this stuff (though with much bigger numbers ) massive approximations are pretty much normal... to the point I carried all components through for each calculation.	”

Thats possible. Sometimes, solutions and equations are presented in terms of the components, such as n = ax + by + cz in cartesian where x, y, and z represent the vector components (youd recall them by them having a little "hat" on top of the letter). I imagine it might even be preference of the person who asks for the solution. Its just that from a intuitive perspective, a single calcuated vector based on the components and plotted is much more useful to a human trying to discern information from it.

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PlumDragon Herbs: Dit Da Jow and Iron Palm Liniments

"When a handshake passes the elbow, it becomes Judo."

looking out some old code (more interesting than watching jobs run) to pull out the formulas (and then try and convert them from geodetic to mass centre) it occured to me this is the perfect example of the "gaze heuristic"

Gut Feelings: The Intelligence of the Unconscious - Times Online

"If consciously performed, catching a ball would involve juggling with differential equations in our heads. We have acquired through evolution, he argues, a prodigious number of adaptive “short cut” capacities, accumulated over the ages by the brain and central nervous system. In the case of catching a ball, the evolutionary trick is what he calls the “gaze heuristic”, a “keep your eye on the ball” tactic"...

Looking at the physics like this is a useful reminder of the reason martial artists sometimes use unscientific but effective shortcuts - like saying "sink" rather than going through the angles and equations involved in lowering the centre of gravity.

__________________
Consider Phlebas, who was once handsome and tall as you
High mountains are a feeling
I don't need to sell my soul, he's already in me