We begin our exploration of mechanics by learning how to describe motion without asking why the motion takes place. This part of mechanics is called kinematics. For simplicity we start off limiting ourselves to motion along a straight line, one dimensional motion.
To illustrate the techniques we use to describe motion we have brought in a track on which a little cart can move. We shall focus on two simple types of motion along the track. Motion at constant speed and motion at constant acceleration. To characterize the motion we shall register the position of the cart as a function of time. For this purpose we have a set up photo-gates along the track which register the time at which the cart first interrupts the light path. Since I know where the photo-gates are I end up measuring the location of the cart in a position-time coordinate system.