4. Dynamics

Dynamics provides the link between the motion of a body, described by kinematics, and the actions causing that motion.

Newton’s principles of dynamics and the cardinal equations of dynamics are the physical laws that govern the motion of mechanical systems: Newton’s principles agree with the experimental observations (for systems with negligible quantum and Einstein relativity effects) and are the starting point - the principles - of Newton’s formulation of mechanics; from these principles, equations of motion of mechanical systems are derived. These physical laws are formulated in terms of certain physical quantities, such as momentum, angular momentum, or the kinetic energy of the system - already discussed in the section about inertia. These dynamic quantities have the property of being additive (by definition), and making it particularly easy to write and interpret a general form of the equations governing motion. In general, these equations relate the time derivatives of these dynamic quantities to the causes of their variation. In the absence of net causes, conservation principles hold.