A complex body is an aggregate of spring-mass systems. The force acting on each mass in the body is a function of that mass multiplied by the acceleration. If a body is accelerated by a steady, homogenous field, all of the spring-mass systems maintain their space relationships with the other spring-mass systems. However, if the acceleration of a complex body is not steady (i.e.. If the jerk is not zero.) some of the spring-mass systems that make up the body are set into motion. This is an uncomfortable and sometimes harmful condition that people generally try to avoid. Whiplash is the most common injury caused by large jerk conditions.

Note that Jerk has the dimensions of momentum density * G.