Table of Contents
What is velocity?
The rate of change of position of an object with time in a given direction is called its velocity. It can also be defined as the speed of an object in a given direction. It is equal to the displacement covered per unit time.
Velocity = Displacement / Time
As velocity has both magnitude and direction, it is a vector quantity. Velocity can be positive, zero or negative depending on the displacement is positive, zero or negative.
Units of velocity
The SI unit of velocity is ms-1.
The CGS unit of velocity is cms-1.
The dimensional formula for the velocity is [M°L1T-1].
Different Types of Velocities:
(i) Uniform velocity
A body is said to be moving with uniform velocity if it covers equal displacements in equal intervals of time, however small these time intervals may be.
(ii) Variable velocity
A body is said to be moving with variable velocity if either its speed changes or direction of motion changes or both change with time.
(iii) Average velocity
For an object moving with variable velocity, average velocity is defined as the ratio of its total displacement to the total time interval in which that displacement occurs.
Average velocity = Total displacement / Total time
If x1 and x2 are the positions of an object at times t1 and t2, then the average velocity from time t1 to t2 is given by
Vav = Δs/Δt
(iv) Instantaneous velocity
The velocity of an object at a particular instant of time or at a particular point of its path is called its instantaneous velocity. It is equal to the limiting value of the average velocity of the object in a small-time interval taken around that instant, when the time interval approaches zero. Thus
V = ds/dt
Thus, instantaneous velocity of an object is equal to the first order derivative of its displacement with respect to time.