Bruce Lee’s Superhuman One-Inch Punch | Hacker News Reader

Bruce Lee’s Superhuman One-Inch Punch

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12 pointsAnon848 comments

So as a student of Martial Arts myself, i had thought of many applications of Physics to how power is actually generated. While this article is quite detailed i think they have sort of obscured the main points. The following are some Physics concepts relevant to Martial Arts;

1) Difference between Force and Pressure (Force/Area) - This is why a finger jab is more effective than a slap and why punching with two knuckles is more devastating than punching with the entire front face of the fist. A good example is the ease with which you can pierce wood with a sharp nail vs. a blunt one.

2) Impulsive Force (mv-mu)/t - This is the reason you pullback the striking fist as quickly as possible. Note that the change in momentum due to the reversing of direction evaluates the numerator as (mv - (-mu)) = mv+mu along with the denominator t being made as small as possible thus resulting in a larger force. A good example is the game of Billiards/Carrom.

3) Moment/Couple/Torque - This is the reason the side of the body opposite to the striking side is pulled back, waist is twisted and the striking fist uses a screwing motion from palm up to palm down position. The body is kept stable, centered and the force focused. The best example is the classical Karate punch where the non-striking hand is pulled back parallel to the striking hand while both fists follow a screwing/unscrewing twist.

4) Newton's 3rd law - This is why while punching you forcefully push the ground with your rear leg at an angle and twist your waist. The rear leg pushing the ground causes the ground to push back with an equal and opposite force along the leg which is at an angle to the ground. This Force vector can be decomposed into two perpendicular vectors one acting vertically against gravity and the other horizontally in the direction of the strike. This horizontal force is then channeled by the twisting of the waist to the shoulder, hand and fist.

It is all just Physics and Body Dynamics; nothing "Superhuman" :-)

Great write up, have you seen any examples in modern MMA of the techniques you brought up?

There are lots more Physics principles with application nuances involved which one can find in many Sports Anatomy/Physiology books though i am not aware of any dealing with Martial Arts techniques exclusively (i had worked out the above for myself).

Many Athletes/Coaches (MMA or otherwise) know of these to a certain degree by traditional teaching methods or instinct even though they might be unaware of the Physics behind it. For example a Boxing coach might say "put the Body into the punch" , a Karate instructor might say "power comes from twisting the Hip", a Judo coach might say "keep your center of gravity low and close to the opponent's" etc. Because our Body dynamics can be so complex (due to our many joints) different Martial Arts emphasize different methods of generating force eg. A Boxing punch vs. Karate punch, A KungFu snap kick vs. a Muay Thai sledgehammer kick etc.

Because Martial Arts development was more empirical, the old texts (there is great value in reading these texts) often mention techniques which are proven to be highly effective which we now can try and explain using Modern Physics principles.

> 2) Impulsive Force (mv-mu)/t - This is the reason you pullback the striking fist as quickly as possible. Note that the change in momentum due to the reversing of direction evaluates the numerator as (mv - (-mu)) = mv+mu along with the denominator t being made as small as possible thus resulting in a larger force. A good example is the game of Billiards/Carrom.

This reasoning would suggest that if you put two billiard balls next to each other and pull one of them away, conservation of momentum will result in the other rolling away in the opposite direction at the same speed. I've never seen that happen, and not just because I suck at billiards. When you pull the ball/your fist away, that changes the momentum of your body, not the other ball/your opponent's body that you're now no longer in contact with.

Your reasoning is wrong. When at rest the momentum of both balls is zero and when you pull one ball away from the other the change in momentum (and hence the force) is opposite to the other ball. Thus there is no collision and transfer of energy i.e. each is independent.

It is only at the point of collision that the impulsive force is imparted to the other body.

See this Khan Academy video "Impulse and momentum dodgeball example" for detailed understanding: https://www.khanacademy.org/science/physics/linear-momentum/...

Also see article "Momentum Change and Impulse Connection" (note the Rebounding Collison section at the bottom) : https://www.physicsclassroom.com/class/momentum/Lesson-1/Mom...

> when you pull one ball away from the other the change in momentum (and hence the force) is opposite to the other ball. Thus there is no collision and transfer of energy i.e. each is independent

Indeed, that was my point. Because "reversing of direction evaluates the numerator as (mv - (-mu)) = mv+mu along with the denominator t being made as small as possible thus resulting in a larger force" is incorrect for the same reason.

No, you still have not understood it; what i am pointing out is a change in momentum after a collision resulting in the Impulsive Force.

See the Khan Academy video i linked for a detailed example with numerical calculations; It walks you through the steps involved.

Also from my 2nd linked article;

Observe that each of the collisions above involve the rebound of a ball off a wall. Observe that the greater the rebound effect, the greater the acceleration, momentum change, and impulse. A rebound is a special type of collision involving a direction change in addition to a speed change. The result of the direction change is a large velocity change.

https://archive.is/ocam3

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