Retardation/deceleration is defined as the acceleration in the direction opposite to the direction of the velocity. Retardation and deceleration are same thing. Retardation/deceleration causes decrease in velocity.
| Symbol | \vec{a},a |
| S.I. Unit | m/s2 |
| Dimension | LT-2 |
| Vector/Scalar | Vector |
| Fundamental/Derived | Derived |
Table of Contents
Retardation and negative acceleration
Retardation/deceleration refers to acceleration in the opposite direction to that of motion whereas negative acceleration means acceleration in the negative direction of a pre-defined co-ordinate system. Negative acceleration may or may not be retardation/deceleration. Retardation/deceleration may or may not be negative acceleration.
Lets understand it better from the example given below.
1. Fig A :– The car is moving with increasing velocity from A to B. Here the it has positive (+) acceleration as it is accelerating in the positive direction (X) of the pre-determined co-ordinate system.
2. Fig B :– The car is moving with decreasing velocity from A to B. Here it has negative (-) acceleration as it is accelerating in the negative direction (X’) of the pre-determined co-ordinate system . The car is also decelerating because the acceleration is opposite to the direction of motion.
3. Fig. C :– The car is moving with increasing velocity from A’ to B’. Here its acceleration will be taken as negative (-) as it is accelerating in the negative direction (X’) of the pre-determined co-ordinate system .
4. Fig. D :– The car is moving with decreasing velocity from A’ to B’. Here it has positive (+) acceleration as it is accelerating in the positive direction (X) of the pre-determined co-ordinate system. The car is also decelerating because the acceleration is opposite to the direction of motion.
In Fig. C though the car has negative acceleration it is increasing its speed and in Fig. D though the car has positive acceleration it is decreasing its speed.
Uniform deceleration/retardation:
When a body decreases equal velocity in equal interval of time, the acceleration is called uniform deceleration/retardation.
velocity ~ time graph:
acceleration ~ time graph:
