1.1.1 Making a Motion Diagram

An easy way to study motion is to make a video of a moving object. A video camera, as you probably know, takes images at a fixed rate, typically 30 every second. Each separate image is called a frame. As an example, FIGURE 1.2 shows four frames from a video of a car going past. Not surprisingly, the car is in a somewhat different position in each frame.

FIGURE 1.2 Four frames from a video.

The figure depicts the motion of a car in four frames of a video placed one below the other.
FIGURE 1.2 Full Alternative Text

Suppose we edit the video by layering the frames on top of each other, creating the composite image shown in FIGURE 1.3. This edited image, showing an object’s position at several equally spaced instants of time, is called a motion diagram. As the examples below show, we can define concepts such as constant speed, speeding up, and slowing down in terms of how an object appears in a motion diagram.

FIGURE 1.3 A motion diagram of the car shows all the frames simultaneously.

The figure illustrates the motion diagram of a car approaching a tree.
FIGURE 1.3 Full Alternative Text

NOTE   It’s important to keep the camera in a fixed position as the object moves by. Don’t “pan” it to track the moving object.

NOTE   Each chapter will have several Stop to Think questions. These questions are designed to see if you’ve understood the basic ideas that have been presented. The answers are given at the end of the book, but you should make a serious effort to think about these questions before turning to the answers.