Displacement is the difference between the final position, xf, and the initial position, xi.
A displacement to the right will be a positive displacement. That is,
x > 0 since
xi < xf .
For example, starting with xi = 60 m and ending at xf = 150 m, the displacement is
x = xf - xi = 150 m - 60 m = 90 m
A displacement to the left will be a negative displacement. That is,
x < 0 since
xi > xf .
For example, starting with xi = 150 m and ending at xf = 60 m, the displacement is
x = xf - xi = 60 m - 150 m = - 90 m
Positions to the right of the origin are positive.
Positions to the left of the origin are negative.
Distance is the absolute value of the displacement. Distance is always positive and tells how far something is from something else but does not tell us whether it is to the right or to the left.
You might give the displacement of some object as x = - 15 m. To describe the same thing in terms of distance you must say something like "it is located at a distance of 15 m, to the left of the origin".
Units are important in Physics (and in all of Science). In the lab, we will usually measure distance or displacement in units of meters (m). Distance or displacement could also be measured in centimeters (cm) or kilometers (km) or even miles (mi).
(c) Doug Davis, 2001; all rights reserved