Thread: Martial Arts Physics

Alright, I've been trying to find the right physics theories to work with, but I've been out of the physics world for a while so maybe y'all can help me.

Here's four examples I'd like to try to explain, in fairly basic physics.

First is a simple punch. How is energy transfered from the body to the fist, through the joints? Is a whip analogy relevant?

Second is a long pole. How does a small movement at one end of the pole (the end you're holding) translate into a larger movement (and hence more power) at the other end (both ends are the same size).

The last two are sort of extra but I'm wondering if maybe they relate. That would be, the whip and a knife throw (which resembles a whip when thrown by a skilled practitioner).

Tying the first and last points: when I teach people to punch I try to use a chain analogy and have them imagine their hand as the last link in the chain (or whip) which then snaps and releases it's energy. The only work done by the muscles should be the initial release of power to propel the fist forward, then the muscles relax so that no energy can slow the strike and no energy wasted if the strike is stopped (and so it cannot be controlled by the opponent, etc. but this goes beyond what I'm really talking about here).

I was running into concepts like angular momentum, conservation of energy, wheels, etc. Can anyone help me link this all together?

And one more thing. I was specifically thinking of a straight punch, but if someone would like to discuss a hook, or do a comparison that would be great too. I would think, in theory, a hook has the potential to be more powerful (just as a round house kick would have more power than a straight one).

-EDIT-
Also, just realized, lever mechanics is probably very important....

If your after power, check out my 7 heart tips! : http://www.thescienceforum.com/7-Heart-Tips!-30791t.php

You wont get so tired, so you can train more!

I'm sorry, but that does not help me at all!

Let me preface by stating that I'm not a physics guy, but I'll try to take a swing at your questions.

Originally Posted by DaBOB

First is a simple punch. How is energy transfered from the body to the fist, through the joints? Is a whip analogy relevant?

The whip analogy helps, yes, but is insufficient in itself. As you seem to be aware already, in the body it is a coordinated cascade of muscle activity which transfers the initial movement from your hips through the abdomen, through your chest, through your shoulders, through your biceps and forearms, and which ultimately launch your fist forward.

Where I see the idea breaking down is that the whip doesn't add energy at each point along the length of the cord, whereas the body does add energy as the motion is transferred. Energy is added (if done properly) as each major muscle group contracts in a coordinated cascading way. A better analogy is perhaps the electricity grid transferring energy from the power station to your home. Along the way are amplifiers on the transmission lines, and your muscles offer a similar amplifying effect as the energy itself is transferred.

Additionally, mass is more of a factor with a punch or a kick (than it is with a whip), and hence so too is momentum. The whip is light, so relies almost entirely on velocity and snap, whereas the fist is heavier and has the backing of the body's mass, so incorporates more fully both velocity and heft. In short, momentum (velocity x mass) is generally going to be higher with a fist even though it's traveling more slowly than the whip. However, you can definitely help add to the effect by having that "snap" in your punch to get a bit of extra velocity/momentum immediately before impact.

Finally, the snap of your fist helps because it allows the maximum amount of energy to be transferred into the target. When you land on the target and push your fist into it, leaving your fist pressed against it, less of the energy stays with the target and some gets reabsorbed by your own fist... it comes back to you. By snapping the punch, much more of it remains in the target since you've pulled the fist away before having a chance to reabsorb as much of the imparted energy.

Originally Posted by DaBOB

Second is a long pole. How does a small movement at one end of the pole (the end you're holding) translate into a larger movement (and hence more power) at the other end (both ends are the same size).

It happens atom by atom, molecule by molecule. The electrostatic pressure of the atoms causes them to repel. As you push one end of the pole, the atoms closest to you compress, and that energy is transferred to the atoms and molecules beside them. Then, those atoms and molecules compress and transfer that energy to the atoms and molecules beside them... and this process repeats over and over and over until that energy has been exhausted, usually at the other side on the far end of the pole... it terminates.

It's basically a small amplitude wave. Like when you pick up one end of a garden hose, raise it high above your head, then slam it downward. It creates a wave which travels along the length of the hose until the energy dissipates. It's roughly the same thing with a more rigid pole or rod. Your pressing one end creates a nearly imperceptible wave which travels all the way down it's length... atom by atom... molecule by molecule... until the energy dissipates... usually at the other end.

The concept I described above about snap with the fist would apply here as well when striking with a rod... The snappier you are, the more energy is left within the target, and the less gets reabsorbed by the striking object.


EDIT: I may have misinterpreted you here, and I see it's possible you could be asking about leverage. If so, he pivot point would be your hand holding the pole, and the pole itself becoming a bit of a lever), like the work Archimedes did. [/EDIT]

Originally Posted by DaBOB

Tying the first and last points: when I teach people to punch I try to use a chain analogy and have them imagine their hand as the last link in the chain (or whip) which then snaps and releases it's energy. The only work done by the muscles should be the initial release of power to propel the fist forward, then the muscles relax so that no energy can slow the strike and no energy wasted if the strike is stopped

Agreed. This is the concept of resistance. The tighter the muscles are, the more energy is lost fighting that tension. By loosening the muscle and relaxing the tension, the energy from the initial movement (usually generated in the hips if done properly) can more freely travel, and hence will move toward your opponent with greater velocity... less will be wasted trying to overcome the resistance offered by the contracted muscles.

Originally Posted by DaBOB

I was running into concepts like angular momentum, conservation of energy, wheels, etc. Can anyone help me link this all together?

This is a bit beyond my depth. Perhaps an actual physicist can address this, and even correct me if I've misspoken with anything above.


Also, it occurs to me that this topic may get a stronger response in the biology section of the forum. Just food for thought. Cheers.

Originally Posted by DaBOB

And one more thing. I was specifically thinking of a straight punch, but if someone would like to discuss a hook, or do a comparison that would be great too. I would think, in theory, a hook has the potential to be more powerful (just as a round house kick would have more power than a straight one).

I disagree with your assessment here. Mass is critical when determining the power of a strike, and when you throw a hook there is much less body mass behind it. You lose a lot of the underlying mass energy coming from the hips, legs, chest, and even shoulders. However, when you throw a straight punch or a cross, you have the mass of the body much more fully involved with reinforcing the strike, and all of those muscles coming together in aggregate to support the impact. Perhaps you can throw the hook at a higher velocity than the straight punch, but I'd be reluctant to think that it's fast enough to make up for the loss of mass.

Also, above I forgot to mention the concept of hydraulic shock (also sometimes called fluid shock), and the shockwave or ripple effect which relates to striking. The body is mostly water, and you can generate something resembling a wave, complete with it's crashing energy. This is probably the closest to your analogy of a whip. When I trained, we used to refer to something called the three harmonies, and how different parts of the body should move in conjunction with each other to have the greatest effect... hips move with the shoulders, elbows move with the knees, and wrists move with the ankles. When these pairings are coordinated properly, the energy from the fist or striking foot is at it's highest.

We also frequently reviewed placement of the strike, and proper penetration depth when visualizing the target (we spoke also of pressure points, but I'm not referring to that here... just whether you aim aim behind the target instead of for its surface, for example). It is better to punch "through" the person than "at" the person. I think that relates to displacement somehow, but I don't understand it well enough to offer anything on that for you here.

Cheers.

Originally Posted by DaBOB

Alright, I've been trying to find the right physics theories to work with, but I've been out of the physics world for a while so maybe y'all can help me.

Here's four examples I'd like to try to explain, in fairly basic physics.

First is a simple punch. How is energy transfered from the body to the fist, through the joints? Is a whip analogy relevant?

Second is a long pole. How does a small movement at one end of the pole (the end you're holding) translate into a larger movement (and hence more power) at the other end (both ends are the same size).

The last two are sort of extra but I'm wondering if maybe they relate. That would be, the whip and a knife throw (which resembles a whip when thrown by a skilled practitioner).

Tying the first and last points: when I teach people to punch I try to use a chain analogy and have them imagine their hand as the last link in the chain (or whip) which then snaps and releases it's energy. The only work done by the muscles should be the initial release of power to propel the fist forward, then the muscles relax so that no energy can slow the strike and no energy wasted if the strike is stopped (and so it cannot be controlled by the opponent, etc. but this goes beyond what I'm really talking about here).

I was running into concepts like angular momentum, conservation of energy, wheels, etc. Can anyone help me link this all together?

The thing that can be tough sometimes for students learning martial arts to understand is that there is a big difference between kinetic energy and momentum.
A 400 gram bullet traveling at 250 meters per second has only one tenth the momentum that a 200 kilo-gram NFL linebacker charging at 5 meters per second would have. However, the bullet's kinetic energy is five times greater than the linebacker's kinetic energy. That's a good part of the reason why bullets are lethal, and charging linebackers are (usually) not.

So, from a destructive standpoint, speed matters more than mass. A typical brawler will punch you in a way where their muscles are rigid, so as to throw all of their weight into the punch, but in Karate (which is the area I studied), you're going for a fast punch instead, and tightening your arm muscles would slow your fist down. Only the weight of your fist (and maybe your forearm) connects, rather than the weight of your whole body, but it connects at a much faster speed, and therefore causes more damage.

As far as the long stick and whip, the advantage in both cases is the ability to impart speed to the end, by using a large amount of mass (your body) to set a small amount of mass into motion (the mass of the tip or end).

I would like to get more into the hard physics, but I think I should probably put in some of my own work here. Don't have the time just now though.

Also, I agree there is an important distinction being made here regarding velocity and momentum. What I meant by a hook being more powerful was actually exactly what you said, more velocity. Of course, this would probably depend on the practitioner, I'm just speaking theoretically.

I think I agree with everything else here. I'll add more commentary and update as I work some things out on my own.