Purpose 1. To learn how speed is related to distance and time and explore a method using photo gates to measure constant speed. 2. To plot a graph of distance versus time, find the slope, and interpret it as a speed. Theory In one-dimensional motion the object moves along a straight line, for example along the x direction. If the object is changing its position uniformly with time it is in constant-velocity motion. Velocity is defined as the time rate of change of displacement. In the case of motion with constant velocity, the position of the object ( ) at time, t, can be determined as: where is the initial position and is the velocity. The quantity - gives the displacement. So, from Eq. (1), and therefore or, in words, speed = distance travelled /time elapsed. In today's lab the distance that we need to use is the distance traversed between two positions; i.e., the change in the distance. So we should really say speed = change in distance /elapsed time (3) (That is why we write in Eq. (1) and in Eq. (2).) If we let the displacement, , be represented by d (standing for the displacement, or change