2.3: Distance and Displacement

Distance describes how much an object has moved. It depends on how the object has moved, that is, the path the object took to get from the starting point to the ending point. The units for distance pertain to length, such as meters. Distance is a scalar quantity because it describes the magnitude of the measurement, but not a specific direction.

Displacement describes an object's overall change in position. It only depends on the starting and ending points of the object. It does not depend on the path taken to get between the two points. Like distance, the units for displacement are also length, such as meters. However, displacement is a vector quantity, which means it has a magnitude and a specific direction associated with the measurement. So, the complete value for displacement must also include a direction.

For an example, consider a four-story building. A person needs to travel on the elevator from the first to the third floor. To accomplish this, the person could take an elevator directly from the first floor to the third floor. In this case, the distance and displacement are the same, because the person went directly from the starting to the ending point.

However, this is not the only way the person could travel from the first to the third floor. They could accidentally hit the fourth floor button when they got on the elevator. In this case, they would travel from the first floor to the fourth floor, and back down to the third floor. In this instance, the displacement is still from the first floor to the third floor. But, the distance is longer, because the person took a detour to the fourth floor before going back down to the third floor.