Physics Class 11 Chapter 3. Motion in a Straight line | Page 5

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Instantaneous Velocity and Instantaneous Speed Instantaneous velocity describes how fast an object is moving at different instants of time in a given time interval . It is also defined as average velocity for an infinitely small time interval .
Here lim is taking operation of taking limit with time tending towards 0 or infinitely small . dx / dt is differential coefficient – Rate of change of position with respect to time at an instant .
Instantaneous speed is the magnitude of velocity . Instantaneous speed at an instant is equal to the magnitude of the instantaneous velocity at that instant .