The terms “distance” and “displacement” are fundamental quantities in Physics used, starting from the most basic to the most complex formulae. Distance and displacement both describe the motion of objects. While they are related, they have distinct definitions and methods of measurement. Let’s explore the differences and similarities between these two.
Distance: Distance is a scalar quantity that refers to the total length covered by an object during its motion. It represents the actual path travelled, regardless of the direction. When not at rest, distance is always greater than zero. Although it can be measured in variety of ways, including meters (m), kilometers (km), or miles (mi), its SI unit is meters (m).
Displacement: Displacement is a vector quantity that refers to the change in the position of an object from its initial point to its final point. It is always the shortest path between two points which is always a straight line. It includes both the magnitude (distance) and direction of the change. Displacement can be positive, negative, or zero, depending on the direction of the motion. Although it can be measured in a variety of ways, including meters (m), kilometers (km), or miles (mi), its SI unit is meters (m).
From the above definitions, we can infer two differences:
1. Distance is the actual path travelled and displacement is the shortest path between the initial and final position which is always a straight line.
2. Distance is scalar (only magnitude) and displacement is a vector (magnitude and direction) which leads to distance always being positive and displacement being negative, zero, or positive.
Let’s look at an example to understand these differences better:
Figure 1.1
Example: Look at the park in Figure 1.1 and imagine that a person walks in a straight path from the playground to the drinking fountain, then back to the playground, and then finally to the lost and found.
Distance has to be the sum of the distances of all the paths travelled and should not consider direction, which in this case would be 85+85+10 = 180 meters since they are walking twice between the playground and the drinking fountain before heading to the lost & found.
Figure 1.2
To find displacement we need to consider the shortest path (straight line) between the starting and ending points and the direction. The person’s starting position is the playground, and the ending position is the lost & found and the shortest path between the two as shown by the straight line on the map is 10 meters. 10 is the magnitude, so we need to find the direction. To understand direction, look at Figure 1.2 above. It indicates that from a given point, movement in one direction is positive and movement in the opposite direction is negative so if we apply that in this context and consider movement towards the drinking fountain from the playground as positive and movement towards the lost & found from the playground as negative, we know that the shortest path is going in the negative direction hence the displacement here is -10 meters as shown in Figure 1.3 below.
Figure 1.3
And that is distance vs displacement explained to you. Head over to the articles section to learn more interesting concepts.
Comments