You must have heard the terms distance and displacement. Let us discuss the difference between the two. We will also discuss the characteristics of displacement.
1. Distance: The actual length of the path covered by a body in moving from one position to another is called distance traveled by the body. Suppose you move in a square shaped ground (each side 100 m) from east to west, then from west to east at the same point. The total distance covered will be 200 m. It is a scalar quantity. It is measured in centimeters (cm) in the CGS system and in metres (m) in the M.K.S system or SI units. The distance covered by a body in motion can never be zero or negative.
2. Displacement: Displacement of an object in a given interval of time is defined as the change in its position in a particular direction during that time. It is the shortest or the straight line distance between the initial an the final positions of the object.
In the above mentioned example of square ground, the total displacement is zero.
Displacement is a vector quantity. It is represented by an arrow with its tail at the initial position and head at the final position of the object. The length of the arrow gives us the magnitude of displacement and the arrow head gives its direction. For example, if an object moves from A to C along the path ABC, then its displacement is . The arrow head at C indicates that the object is displaced from A to C.
It should be noted that the distance covered by a body may be more than its displacement. For example, if a body moves from its initial position A to the final position B along a zig-zag path as shown in the figure, then the distance covered by the body is more than its displacement.
Similarly if a body is moving in a circle of radius r, then distance covered by the body in none rotation = 2pr but displacement of the body in one rotation = zero
Characteristics of displacement:
(i) The unit of displacement is the same as that of length.
(ii) The displacement of a body in a given time interval can be positive, negative or zero.
(iii) Displacement is a vector quantity.
(iv) The magnitude of displacement of a body between two points gives the shortest distance between these points.
(v) The displacement of a body does not depend upon the choice of origin.