Graphical Interpretation - Space Time Diagrams
- A Space-Time diagram is constructed when one spacial axis is replaced with time and the object's equation of motion x(t) is plotted as a curve on that diagram.
- A Space-Time diagram gives a visual picture of the motion of an object as a function of time. Even when the motion is complex, it is useful to see what is happening to object's location as function of time.
- A Space-Time diagram could be looked at as being constructed from a motion picture of the object's movement over time. By cutting the resulting film strip up into individual frames and then placing them side by side along the t-axis would produce a space-time diagram of the object's motion.
- The curve of an object's equation of motion on a space-time graph is called a worldline. A single point on that curve is called an event; it simultaneously represents both a location and time.
- Straight worldlines on a space-time diagram represent uniform motion, i.e. the object is moving at a constant speed.
- The slope of the worldline is equal to the velocity of the object at that moment.
- A Space-Time diagram is purely conceptual -- you cannot look out a window and see a car or a rock following a distance versus time curve.
- A horizontal worldline on a space-time diagram represents no motion at all -- the object is at rest.
- It is tempting to talk about an object's motion along its worldline on a space-time diagram. Doing so invokes the idea of some "super-time" which is related to the rate at which an object moves through time -- a meaningless concept unless you assert that it is always uniform, i.e. that mother nature does not speed up or slow down the rate at which nature's camera is running. A worldline represents a "frozen space-time" picture in that it simultaneously contains the total history of the object motion through space as a function of time.
