Space, time and motion

Abstract

You are undoubtedly familiar with motion in all kinds of manifestations, but what would you say if you were asked to define it? The chances are that you would find yourself formulating a statement in which the phrase ‘a change of position with time’, or something equivalent to that, expressed the central thought. For it seems that our ability to give any precise account of motion depends in an essential way on the use of the separate concepts of space and time. We say that an object is moving if it occupies different positions at different instants, and any stroboscopic photograph gives vivid expression to this mental picture.