In physics, motion is a change in position of an object with respect to time also on its reference point. Motion is typically described in terms of displacement, distance (scalar), velocity, acceleration, time and speed. Motion is observed by attaching a frame of reference to a body and measuring its change in position relative to that frame. If the position of a body is not changing with the time with respect to a given frame of reference the body is said to be at rest, motionless, immobile, stationary, or to have constant (time-invariant) position. An object’s motion cannot change unless it is acted upon by a force, as described by Newton’s first law. Momentum is a quantity which is used for measuring motion of an object. An object’s momentum is directly related to the object’s mass and velocity, and the total momentum of all objects in an isolated system (one not affected by external forces) does not change with time, as described by the law of conservation of momentum. The study of motion deals with (1) The study of motion of solids (mechanics). (2) study of motion of fluids (fluid mechanics) As there is no absolute frame of reference, absolute motion cannot be determined. Thus, everything in the universe can be considered to be moving . More generally, the term motion signifies a continuous change in the configuration of a physical system. For example, one can talk about motion of a wave or a quantum particle (or any other field) where the configuration consists of probabilities of occupying specific positions.
