Table of Contents
Distance or path length
It is the length of the actual path traversed by a body between its initial and final positions. As shown in Fig. 3.4, suppose a body moves from position A to B through C. Then
Distance covered = AC + CB
Important Points Regarding Distance:
Distance is a scalar quantity because it has only magnitude and no direction. Distance covered is always positive or zero.
Units of Distance
The SI unit of distance is metre (m).
The CGS unit of distance is centimetre (cm).
Displacement
The displacement of an object is the change in the position of an object in a fixed direction. It is the shortest (or the straight line) path measured in the direction from initial point to the final point. As displacement has both magnitude and direction, so it is a vector quantity.
In Fig., displacement = AB
Important Points Regarding Displacement:
Displacement may be positive, negative or zero.
Units of Displacement
The SI unit of displacement is metre (m). The CGS unit of displacement is centimetre (cm).
Characteristics of Displacement
(i) Displacement has the units of length.
(ii) The displacement of an object can be positive, negative or zero.
When an object moves towards right, its displacement is positive.
When an object moves to the left, its displacement is negative.
When an object remains stationary, or it moves first towards right and then an equal distance towards left, its displacement is zero.
(iii) Displacement is not dependent on the choice of the origin O of the position coordinates.
(iv) The actual distance travelled by an object in a given time interval is greater than or equal to the magnitude of the displacement.
(v) The displacement of an object between two points is the unique path that takes the body from its initial to final position.
(vi) The displacement of an object between two positions does not give any information regarding the shape of the actual path followed by the object between these two positions.
(vii) The magnitude of the displacement of an object between two positions gives the shortest distance between these positions.
(viii) Displacement is a vector quantity. Displacement of an object between two given positions is independent of the actual path followed by the object in moving from one position to another.