CBSE
Class 10
Class 12
Instantaneous speed: It is the speed of a particle at a particular instant.
The instantaneous speed is the average speed for an infinitesimally small time interval(i.e., ∆t -> 0 ). Thus
Instantaneous velocity: Instantaneous velocity is defined as the rate of change of position vector of particles with time at a certain instant of time.
Comparison between average speed and average velocity
(a) Average speed is scalar while average velocity is a vector both having same units (m/s) and dimensions [LT-1]
(b) Average speed or velocity depends on time interval over which it is defined.
(c) For a given time interval average velocity is single-valued while average speed can have many values depending on the path followed.