Motion (physics)
In physics, motion is a change in position of an object with respect to time. Motion is typically described in terms of velocity, acceleration, displacement, and time. Motion is observed by attaching a frame of reference to a body and measuring its change in position relative to another reference frame.
A body which does not move 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. An object's momentum is directly related to the object's mass and velocity, and the total momentum of all objects in a closed system (one not affected by external forces) does not change with time, as described by the law of conservation of momentum.
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.
Read more about Motion (physics): Laws of Motion, Kinematics, List of "imperceptible" Human Motions, Light, Types of Motion
Famous quotes containing the word motion:
“The motion picture is like a picture of a lady in a half- piece bathing suit. If she wore a few more clothes, you might be intrigued. If she wore no clothes at all, you might be shocked. But the way it is, you are occupied with noticing that her knees are too bony and that her toenails are too large. The modern film tries too hard to be real. Its techniques of illusion are so perfect that it requires no contribution from the audience but a mouthful of popcorn.”
—Raymond Chandler (1888–1959)