Question

What do you mean by retardation. What is its unit?

Answer 1

Hint: Retardation is another name for deceleration. Deceleration is a vector quantity that can act on a moving body such that it reduces the magnitude of the velocity (speed) of the body. So, we can say that deceleration is an acceleration that is directed opposite to the velocity vector of a body.

Complete step by step answer:
We know that when an external force acts on a body it accelerates or decelerates the body. Acceleration can be defined as the rate of change of velocity with time.
 If the change in velocity is positive in a time interval, i.e. when final velocity is greater than the initial velocity in that particular time interval. We say that the object is being accelerated in that time interval.
If the change in velocity is negative in a time interval, i.e. when final velocity is lesser than the initial velocity in that particular time interval. We say that the object is being decelerated in that time interval.
This deceleration is also known as retardation since it decreases the velocity of the body. So the deceleration is the same as retardation and its unit is the same. The unit of deceleration is the same as acceleration, which is meter per second-square $\left( \text{m/}{{\text{s}}^{2}} \right)$.

Note: The deceleration is always associated with a negative sign to signify there is a decrease in velocity during a period of time.
The force which causes retardation is known as the retardation force.
For a body moving in one dimension, we can say that deceleration occurs when the direction or signs of velocity and acceleration are opposite to each other. A negative velocity vector and a positive acceleration vector signifies deceleration, a positive velocity vector and a negative acceleration vector also signifies deceleration.