Evaluation of the effect of momentum on interaction forces in a linked system

Engineering of Sport 15 - Proceedings from the 15th International Conference on the Engineering of Sport (ISEA 2024)

Newton’s first law describes the behavior of an object if no external forces were to act on it and in so doing provides a baseline for understanding the forces applied. In a linked system, a similar counterfactual analysis can show the behavior if supplied joint torques were not present at a given kinematic state. This type of analysis can provide insight into the nature of the system and how the forces seen are affected by its current momentum state. The golfer – club system represents a linked system consisting of multiple joints and segments. At each of these joints a torque can be applied by the golfer to drive the club throughout its movement. The interaction force developed between segments depend on both the torques applied at each joint and the kinematic state of the system and the momentum it contains. A forward dynamics model is used as a basis for evaluating the behavior of the system when applied torques at joints are “turned off” in stepwise fashion across a representative number of time points. Output from these runs were compiled creating a representation of the contribution of momentum to joint interaction forces at each point in time. This analysis separates the contribution of “what has already been done” (forces created through interaction of momentum) from “what is currently being done” (forces created by applied joint torques) to generate the total force observed at the joints in a linked system. This is similar to the effect of initial conditions on the solution of differential equations.