WEEK 4: Position, Distance and Displacement

The Concept of Position

The position of an object is its location in space. It is usually expressed in relation to a reference point. To locate an object in space, a co-ordinate system is needed. It is usually a mathematical construct with co-ordinates.

A coordinate system could be two-dimensional as in P(x,y) or three dimensional as in P(x,y,z).

The Concept of Distance and Measurement

Distance can be defined as a physical measurement of length between two points. It does not take into consideration the direction between the two points it measures; hence, it is a scalar quantity. This therefore means that distance has only magnitude but no direction. E.g, 10km.

Distance could be measured using instruments like measuring tape, ruler, vernier caliper, micrometer screw gauge, etc.

The Concept of Displacement

Displacement is defined as the distance travelled or moved in a specific direction. It takes into consideration the direction between the different points it seeks to measure; hence, displacement is a vector quantity. Thus, it has both magnitude and direction. E.g, 10km due east. The ‘10km’ is the magnitude (or value), while ‘due east’ is the direction.

Both distance and displacement have the same S.I. unit, metre (m). They could also be expressed in kilometre (km), miles, etc.

Distinction between Distance and Displacement

We need to understand the concepts of distance and displacement.  Distance is the gap between two points with no regard to direction. On the other hand, displacement is distance covered in a particular direction. Therefore distance is a scalar quantity while displacement is a vector quantity. The only similarity between distance and displacement is that they have the same unit.  Let us consider a girl who walked and covered a distance of 20m between two points A and B as shown in fig 1 and fig 2 below

The two activities of the girl are not exactly the same. In both figs. 1 and 2, she covered a distance of 20m. If we are only interested in the distance covered, we can conclude that she did the same thing in fig. 1 and 2 i.e she covered the same distance (20m). If we are interested in both distance and direction, then her displacement in fig. 1 and 2 are not the same. In fig.1 she covered a distance of 20m due east while in fig.2, she covered a distance of 20m due west.   From these, we see that distance is a scalar quantity because it has magnitude only while displacement is a vector quantity because it has both magnitude and direction.

Summarily, the table below shows the difference between distance and displacement

EVALUATION

1. Define distance.
2. What is displacement?
3. State the SI unit of distance.
4. Differentiate between distance and displacement.
5. Why is 5km due east a displacement?
6. Enumerate the measuring devices for distance.