What is displacement in Physics mean?

If an object moves relative to a reference frame—for example, if a bus moves in the forward direction relative to the road, or a passenger moves toward the driver of a bus—then the object’s position changes. This change in position is known as displacement. The word displacement implies that an object has moved, or has been displaced.

Displacement is defined to be the change in position of an object. It can be defined mathematically with the following equation:

Displacement = Δx = xf − x0

Xf refers to the value of the final position.

x0 refers to the value of the initial position.

Δx is the symbol used to represent displacement.

Displacement is a vector. This means it has a direction as well as a magnitude and is represented visually as an arrow that points from the initial position to the final position. For example, consider the professor that walks relative to the whiteboard in the following figure.

A professor paces left and right while lecturing. The +2.0m displacement of the professor relative to Earth is represented by an arrow pointing to the right. (Image credit: Openstax College Physics)

The professor’s initial position is x0=1.5 m and her final position is xf=3.5m. Thus, her displacement can be found as follows, Δx=xf−x0=3.5 m−1.5 m=+2.0 m. In this coordinate system, motion to the right is positive, whereas motion to the left is negative.

What’s confusing about displacement?

Distance and Displacement can be different. By magnitude, we mean the size of the displacement without regard to its direction (i.e., just a number with a unit). For example, the professor could pace back and forth many times, perhaps walking a distance of 150 meters during a lecture, yet still end up only two meters to the right of her starting point. In this case her displacement would be+2m, the magnitude of her displacement would be 2m, but the distance she traveled would be 150m. In kinematics we nearly always deal with displacement and magnitude of displacement and almost never with distance traveled. One way to think about this is to assume you marked the start of the motion and the end of the motion. The displacement is simply the difference in the position of the two marks and is independent of the path taken when traveling between the two marks. The distance traveled, however, is the total length of the path taken between the two marks.