Dynamics is the subdivision of mechanics that describes the forces responsible for motion in classical physics. Since it deals with causes of motion, the study of dynamics leads to concepts of mass (defined as an object's resistance to being moved), work (energy required to move an object a certain distance), inertia (the tendency of a body to resist any attempt to change its state of motion), energy (the capacity to do work), and power (the amount of work done in a given time interval). The study of dynamics is also important for the modern understanding of quantum mechanics and for describing the motion of waves.

The original equations of dynamics are Newton's laws, which describe how bodies respond to an external force. Newton's first law states that a body at rest stays at rest, and that a body in motion stays in motion with a constant velocity, if...