Studying the motion of objects involves the basic techniques of measurement that we learned in the previous chapter. The only units needed are length and time , so at first glance you might expect this study to be quite simple. As you will see, however, limiting our measurements to just two of the fundamental units does not make the mathematics and calculations all that trivial. As is the case in most situations, the keys to understanding this chapter are the definitions of the terms used to describe motion. In this section the most important terms are distance and displacement.
Distance is the actual path length traveled by a moving object.
Displacement is the straight-line separation between the starting and ending positions for the segment of motion under study. In addition, displacement has a specific direction associated with it, which means that it must be treated as a vector quantity. Velocity Once the important distinction between distance and displacement has been learned, the concepts of speed and velocity can be defined by using the interaction of time with changes in position. Velocity is defined as displacement divided by the time and must have magnitude plus direction. This means that velocity must be treated as a vector quantity, just as is displacement.