Let’s continue to look at some simple physics with application to Martial Arts.

Momentum

Momentum depends on mass and velocity.

p = mv

The greater the momentum of a body, the greater its tendency to continue in motion.

Momentum can also be transferred from one person to another.

Kinetic Energy

An object in motion has Kinetic Energy. Kinetic energy (in Joules) depends on the mass and the square of the velocity

KE = ½mv²

Small & Fast or Big and Slow – Which is more dangerous?

Imagine you have a choice of being hit with a sledgehammer weighing 2 Kg travelling at 0.5 metres/sec (m/s) or a pin hammer weighing 0.1 Kg travelling at 10 m/s?

So, they both have the same momentum of 1 Kg m/s

However, the Kinetic Energy of these is different.

Sledgehammer = ½ x 2 x 0.5² = 0.25 Joules

Pin Hammer = ½ x 0.1 x 10² = 5 Joules

So on the face of it, choose the Sledgehammer.

In martial arts, this choice of speed over mass is critical in activities like board breaking, but in an actual combat situation, numerous other factors influence the role of mass versus speed. These different factors include penetration, the target (muscles, bones, or organs ), and the area size of the strike made – for example, a palm heel (large area) or a punch (smaller area).

Traditional martial arts never ask practitioners to become bigger (increase mass), but rather to make the best of what they have naturally, emphasising speed. The techniques are designed to help the smaller person succeed against a bigger attacker.

There is also the problem of what exactly is the mass used in combat, is it the mass of the body or the striking limb or a combination of both? Is this why techniques such as ‘double hip’ or ‘waveforms’ are used to get more of the body mass involved in the strike, because if your velocity is the same then getting a bit more mass in motion is going to increase the KE.

Look at my blog post “Differences – 5: Striking Controversies” for ‘double hip’ and ‘waveforms’.

Potential Energy

Push a rock up a hill and the height that the rock has been raised provides it with the potential to do work by rolling back down under the influence of gravity.

Force = Mass x Gravity.

F = mg

g is the acceleration due to gravity ~ 9.8 metres per second per second

A way to gain extra Kinetic energy in strikes is to additionally use any Potential energy you have. This is why dropping your weight in some techniques can increase their effectiveness.