Position: The location of an object; in physics, typically specified with graph coordinates.

Position tells you location.

There are many ways to describe location: Beverly Hills 90210; “...a galaxy far, far away”; “as far away from you as possible.” Each works in its own context.

Physicists often use numbers and graphs instead of words and phrases. Numbers and graphs enable them (and you) to analyze motion with precision and consistency. In this chapter, we will analyze objects that move in one dimension along a line, like a train moving along a flat, straight section of track.

To begin, we measure position along a number line. Two toy figures and a number line are shown in the illustrations to the right. As you can see, the zero point is called the origin. Positive numbers are on the right and negative numbers are on the left.

By convention, we draw number lines from left to right. The number line could reflect an object's position in east and west directions, or north and south, or up and down; the important idea is that we can specify positions by referring to points on a line.

When an object moves in one dimension, you can specify its position by its location on the number line. The variable x specifies that position. For example, as shown in the illustration for Equation 1, the hiker stands at position x = 3.0 meters and the toddler is at position x = −2.0 meters.

Later, you will study objects that move in multiple dimensions. For example, a basketball free throw will initially travel both up and forward. For now, though, we will consider objects that move in one dimension.