Average speed is defined as the total distance travelled by the body in total time i.e. Average Speed=Total timeTotal distance It is a scalar quantity. Its unit is m/s.
Average Velocity=Total timeTotal Displacement It is a vector quantity and has units of m/s. Magnitude of average velocity is always less than or equal to the average speed because displacement is always smaller than or equal to distance.
Calculating average speed
Average speed is found by first finding the total distance covered by the object and dividing it by the total time taken in travelling the distance. Example: A boy covers a circle of radius 100 m in 100 s. The total distance covered by him will be d=2πr=200πm Average speed will be v=td=100200π=2πm/s
Non-Uniform Speed and Velocity
Non-Uniform Speed : When a body covers unequal distances in equal intervals of time, then that body is said to be in non uniform speed. For e.g., an object thrown into air, like stone, moves at non-uniform speed, lift used to go up or down in a building. Non-Uniform Velocity : When the velocity is not uniform i.e. not constant. This implies that the velocity of the object moving with non uniform velocity is either increasing or decreasing with time i.e. the object is accelerating or decelerating. Since velocity is a vector quantity, hence it depends on two factors namely speed and direction. If any of the two will change, velocity will also get changed. So, we can say that the object is moving with non uniform velocity, if an object is : 1. changing speed wrt time but in the same direction. 2. changing direction wrt time while moving with constant speed.( e.g., motion of a particle in a circular path with constant speed) 3. changing both speed and direction wrt time.