In physics, motion is the change in position of an object or fluid with respect to a reference frame over a given time. Motion is mathematically described in terms of vector quantities such as displacement (with direction and distance), velocity (direction and speed), acceleration, etc. The relative motion of an object with respect to an observer is the object's motion described in the observer's comoving frame, quantified in terms of relative position, relative velocity, etc. The branch of physics describing the motion of objects without reference to their cause is called kinematics, while the branch studying forces and their effect on motion is called dynamics.
If an object is not in motion relative to a given frame of reference, it is said to be at rest, motionless, immobile, stationary, or to have a constant or time-invariant position with reference to its surroundings. Modern physics holds that, as there is no absolute frame of reference, Isaac Newton's concept of absolute motion cannot be determined. Everything in the universe can be considered to be in motion.
Motion applies to various physical systems: objects, bodies, matter particles, matter fields, radiation, radiation fields, radiation particles, curvature, and space-time. The concept of motion also applies to images, shapes, and boundaries. In general, the term motion signifies a continuous change in the position or configuration of a physical system in space. For example, one can talk about the motion of a wave or the motion of a quantum particle, where the configuration consists of the probabilities of the wave or particle occupying specific positions.
