Reference frame

Motion is the process of a body’s displacement in space. Change in the spatial location of a body with respect to a reference is its displacement. Instantaneous motion concerns itself with a body’s behaviour during the instant in consideration. Change of position of a body can be understood only in relation to another body or with respect to a frame of reference or a coordinate system. Depending on the references used or the shapes of paths of displacements, motion is classified into various types. Usually, motion involves instant-by-instant charting of the behaviour of an object. This view reveals not only the instantaneous behaviour of the object but gives a complete picture of it behaviour for a length of time and route and shape of its displacements between initial location and final location. All motions are understood in relation to one or other reference. Since, at present, we have no absolute reference; we use any other seemingly steady body as a reference. Newtonian mechanics consider centre of Solar system as an absolute reference for all purposes related to our planetary system. However, this reference is changed to ‘centre of planet’, while considering the satellite systems and to the surface points on earth for day to day motions of earth-based objects. In rotary motion, centre of rotation is taken as a reference point. Inferences, based on relative reference frame, are often false and apparent. It can provide relative positions of the reference and the referred body. However, if reference body itself is moving, it will not be able to give any other parameters related to an object’s motion or shape of its path. As long as reference frame and referred body have identical initial conditions of motions, they are assumed to be at rest in the relative reference frame. However, this does not reflect any changes within the bodies or their paths due to their real state of motion.