Motion

In physics, motion is a change in position of an object with respect to time and its reference point. Motion is typically described in terms of displacement, velocity, acceleration, 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.

Types of Motion

·        Simple harmonic motion - is a type of periodic motion where the restoring force is directly proportional to the displacement. It can serve as a mathematical model of a variety of motions, such as the oscillation of a spring. In addition, other phenomena can be approximated by simple harmonic motion, including the motion of a simple pendulum as well as molecular vibration.

Example: a pendulum

       

    Periodic motion - in physics, motion repeated in equal intervals of time.

                 Example:  rocking chair, a bouncing ball, a vibrating tuning fork

                                 

      Rectilinear motion (Linear motion) – motion which follows a straight linear path, and whose displacement is exactly the same as its trajectory.

                Example:  apple falling from a tree

                               

         Reciprocating Motion - repetitive up-and-down or back-and-forth motion. It is found in a wide range of mechanisms, including reciprocating engines and pumps. The two opposite motions that comprise a single reciprocation cycle are called strokes

              Example: gears in a machine

                         

·        Brownian motion - is the presumably random moving of particles suspended in a fluid (a liquid or a gas) resulting from their bombardment by the fast-moving atoms or molecules in the gas or liquid.

                Examples: the random movement of particles

                           

 

 Circular motion - is a movement of an object along the circumference of a circle or rotation along a circular path. It can be uniform, with constant angular rate of rotation (and constant speed), or non-uniform with a changing rate of rotation. The rotation around a fixed axis of a three-dimensional body involves circular motion of its parts. The equations of motion describe the movement of the center of mass of a body.

               Examples:  the orbits of planets

                                

·        Rotary motion – a motion about a fixed point.

                    Examples: Ferris wheel

       Curvilinear motion – It is defined as the motion along a curved path that may be planar or in three dimensions.

                     Example: a ball that is thrown

                                         

Rolling motion - is a type of motion that combines rotation (commonly, of an axially symmetric object) and translation of that object with respect to a surface (either one or the other moves), such that, if ideal conditions exist, the two are in contact with each other without sliding.

         Example: the wheel of a bicycle

                

      Oscillation - is the repetitive variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but is sometimes used as a synonym of "oscillation". Oscillations occur not only in physical systems but also in biological systems, from human society to the brain.

                   Example: a spring system is an oscillatory system