Library › 11. Physics in karate › Leverage and torque
Give him a fixed point and he would lift the world off its hinges – so the tradition goes about Archimedes. In karate, an elbow is enough. The principle is called torque: M = F · r (force times lever arm, unit: newton metre). Long lever, little force, big effect.
Levers at the joint
Small force, long arm – and the joint gives way. Joint-lock techniques (Kansetsu-Waza) live on this: if an arm is grasped at the wrist and a pivot is set close to the elbow, a small force acting over the long forearm becomes a large torque on the joint. That is why locks are practised slowly and with control.
Rotation of the body
Throws, evasive movements and the hip rotation in a punch are rotational movements too. A hip throw brings the opponent’s centre of gravity beyond a pivot; one’s own body supplies the lever arm. In the hip rotation, the rotational movement of the trunk is transferred into a linear movement of the arm.
Connection to training
- Pivot close to the opponent’s joint, force far away from it: small effort, big effect.
- One’s own joints are protected by alignment: an extended, “locked” arm transmits force along the bones instead of letting it act as torque on the joint (see Body tension).
- Locks, throws and groundwork are built up in training from slow to real speed.
Sources
- Dieter Meschede (Hg.): Gerthsen Physik. Springer, Berlin/Heidelberg (24. Aufl. 2010, ISBN 978-3-642-12893-6; 25. Aufl. 2015).