Dynamics of spear throwing

The spear thrower (atlatl) is a hunting weapon with very ancient origins. It is a lever that enables wrist rotation to make a substantial increase in the velocity of a thrown spear. A model for throwing a projectile with an atlatl is presented. This model is used to analyze the projectile velocity as a function of the dimensions, rigidity, and mass distribution of the atlatl and mass of the projectile. The model assumes that the throwing force and wrist torque are functions only of the horizontal position of the throwing hand and that the spear is sufficiently long that the atlatl applies only a horizontal force to the proximal end of the spear. The applied force and torque were derived from a high-speed video digitizer plus the known physical dimensions of the atlatl and spear.