Table of Contents
What is acceleration ?
The rate of change of velocity on object with time is called its acceleration. It tells how fast the Velocity of an object changes with time.
Acceleration = Change in velocity / Time taken
Acceleration is a vector quantity. It has the same direction as that of the change in velocity.
Units of acceleration
The SI unit of acceleration is ms-2.
The CGS unit of acceleration is cm s-2.
The dimensional formula of acceleration is [M0L1T-2].
Different Types of Acceleration:
(i) Uniform acceleration
The acceleration of an object is said to be uniform acceleration if its velocity changes by equal amounts in equal intervals of time, however small these time intervals may be.
(ii) Variable acceleration
The acceleration of an object is said to be variable acceleration if its velocity changes by unequal amounts in equal intervals of time.
(iii) Average acceleration
For an object moving with variable velocity, the average acceleration is defined as the ratio of the total change in velocity of the object to the total time interval taken. Suppose v1 and v2 are the velocities of an object at times t1 and t2 respectively, then its average acceleration is
aav = Δv/Δt
(iv) Instantaneous acceleration
The acceleration of an object at a given instant of time or at a given point of its motion, is called its instantaneous acceleration. It is equal to the limiting value of the average acceleration of the object in small time interval around that instant, when the time interval approaches zero. Thus
a = dv/dt = d2x/dt2
Positive and Negative Accelerations
Positive acceleration
If the velocity of an object increases with time, its acceleration is positive. When a bus leaves a bus-stop, its acceleration is positive.
Negative acceleration
If the velocity of an object decreases with time, its acceleration is negative. Negative acceleration is also called retardation or deceleration. When a bus slows down on approaching a bus-stop, its acceleration is negative.