Acceleration

It is defined as the change in the velocity of an object per unit time. If the velocity of an object changes from an initial value u to final value v in time t, then acceleration a is given by Acceleration = (final velocity - initial velocity )/ Time

Properties
SI unit of acceleration is m/s²

It is a vector quantity, its direction is in the direction of change in velocity.

It may be positive, negative or zero.

If an object is moving with constant or uniform velocity, then its acceleration is zero.

Uniform acceleration
A body is said to have uniform acceleration, if it travels in a straight line and its velocity increases or decreases by equal magnitude in equal intervals of time. For example :

(ii) The motion of a bicycle going down the slope of a road (when the rider is not pedaling and air resistance is negligible).

Non-Uniform acceleration
A body is said to have non-uniform acceleration, if its velocity changes by unequal magnitude in equal intervals of time.

For example - The motion of a car on a crowded road.

Retardation or deceleration
A body is said to be retarded if the magnitude of its velocity decreases with time. In this case, the final velocity of the moving body is less than the initial velocity i.e., v<u.

For example - When a person applies brake on a moving car, its velocity decreases with time. For example, if acceleration is a = - 5 m/s ^ 2 we can write this as the deceleration or retardation is taking place at 5 m/s² or you can also put it as acceleration in the opposite direction at the rate of 5 m/s².