Someone said jerk (the third time derivative of displacement) is a
kinematic, not a dynamic quantity. I maintain that is not a useful
point of view. Jerk has important dynamic consequences. Anyone who
thinks otherwise must have failed to notice what happens when one
is standing up in the aisle of a bus and the driver leaves the bus
stop with a jackrabbit start. In this case the kinematic jerk is
the driver, of course, but the change in the direction of the frame
force felt by the standee is dramatic and is the consequence of the
dynamic jerk.