The physics behind Bruce Lee's one-inch punch
A cheeky boy no older than 10 high-fived me as I strolled around the city of Mostar in Bosnia and Herzegovina a fortnight ago.
Then he mimicked a Bruce Lee move. That was not uncommon, as boys in the Balkans, where I travelled to recently, seemed to think every Chinese man is somehow related to Bruce Lee. They then mimic that universally famous 'one-inch punch'.
Astonishingly, Mostar residents are the first, even before Hongkongers, to erect a life-size statue of Lee in their city.
Lee's one-inch punch may be world-renowned, but it's likely that few understand its lethal power.
Besides being a film star who popularised kung fu globally, Lee was one of the fastest and most powerful martial artists of all time.
Standing at 1.7 metres and weighing 61kg, he was clocked delivering a punch at 190km/h. That is equivalent to a high-speed train hitting you in an area no larger than the knuckles of his fist.
Lee's ability to deliver such an immense amount of energy so rapidly made his fists deadly weapons.
To keep himself in top physical condition, he adopted a punishing training regime. But his lethal striking power and lightning speed were derived from wing chun, a Chinese martial art Lee practised early in his martial arts career.
One may well assume that wing chun's scientific principles were the efforts of a physicist or mathematician. But they were actually developed by an 18th century Buddhist nun in China, who was taught by a woman named Yim Wing Chun to defend herself against bullies.
Wing chun is based on simplicity, efficiency and directness. Premised on the fact that women are usually smaller than men, wing chun helps them overcome their handicap in terms of weight and strength by exploiting their greater agility and efficiency of movement to deliver the knock-out punch.
These principles are best expressed in wing chun's basic punch - famously displayed by Lee in 1964 in Long Beach, California.
With his fist moving no more than an inch (2.54cm), he struck a volunteer and sent him careening towards a chair.
But how could so much power be delivered with so little movement by a relative lightweight?
The one-inch punch uses the mathematical principle that the shortest distance between two points is a straight line. Compared to the typical 'round-house punch', which is thrown in an arc towards an opponent, wing chun's basic punch is propelled along a straight line.
In delivering the punch, the wrist is never bent. It is held straight so that the bones in the back of the hand are aligned with those in the wrist and forearm, allowing for the greatest impact supported by the arm, the torso and the legs.
In contrast, a round-house punch has three problems: the punch travels a longer distance to its target and takes a longer time; the risk of self-injury; and the unintended dissipation of shock energy.
The bent wrist in an arc-like motion is prone to injury from the wrist bending back violently upon impact.
Shock energy is dissipated as the punch hits the target at a slanted angle. On impact, the energy from the punch travels forward and sideways. The lateral direction of the force does not contribute to hurting the target. In wing chun's basic punch, all the energy is directed at the target with little or no wasted energy going sideways.
But what about Bruce Lee being relatively small? We usually associate force with size.
Since Newtonian physics tells us that force equals mass times acceleration, to generate a greater force would require a bigger mass - an advantage for larger people. However, force is not what causes damage; it's moving force that creates kinetic energy - that is the transfer of energy from the person throwing a punch at another.
In physics, a moving object's kinetic energy is the product of half of its mass times the square of its velocity. In generating kinetic energy, velocity is more important than mass and has a greater impact since it is a squared term in the equation.
Indeed, a person who weighs half as much as another but punches twice as fast will effect twice as much energy as the bigger person.
Speed is not limited by physical attributes such as weight and height. It can be developed by moving along efficient lines - a key wing chun characteristic. Faster speed makes it harder for an opponent to dodge a punch and delivers a more damaging blow. So the paradox is that you do not have to be fast to fight fast ... if you move efficiently.
Despite its power, fluidity and efficiency, wing chun has the same flaws as other martial arts involving set pieces and movements.
In actual combat, there are no rules. Your opponent will not offer you the chance to deliver your favourite punch. Realising this, Lee developed what he called 'a style without style'. He emphasised minimal movements with maximum effect and extreme speed, without committing himself to any particular martial arts system.
Physicists and system analysts would call that an adaptive dynamics system approach - that is, adapting his style to the circumstances instead of adhering to a predictable format.
Lee called it jeet kune do - the way of the intercepting fist.
Tom Yam is a Hong Kong-based management consultant. He has a doctorate in electrical engineering and an MBA from the Wharton School of the University of Pennsylvania. He has worked at AT&T, Ernst & Young and IBM