What is retardation?
Retardation means negative acceleration . The velocity of a body may increase or decrease .Acceleration takes place when the velocity of a body changes. So when the velocity of a body increase, the acceleration is said to be positive and when the velocity of a body decrease, the acceleration is said to be negative(Retardation) .A body is said to be retarded if its velocity is decreasing.
Eg: a train is said to be retarded when it slows down on reaching a station,i.e. the velocity decreases.Retardation is acceleration with negative sign. Or negative value of acceleration shows that the velocity of a body is decreasing.