Speed v.s Velocity

Speed v.s Velocity

Speed Velocity
Definition The distance moved per unit time. Change in displacement per unit time
Quantity Scalar Vector
Formula speed= (distance moved)/(time taken)
i.e v = d/t		 velocity= (displacement moved)/(time taken)
i.e v = d/t
SI unit m/s m/s
Example A runner runs in the following pathway: A->B->C->D->A. He finishes it within 4 seconds.
Speed = 12 / 4 = 3m/s Velocity = 0 / 4 = 0 m/s
Note
(1) The speed and velocity calculated above are actually the average speed and average velocity for the whole journey. 
(2) When the speed of an object is a constant, its velocity may not be a constant as it can change its direction.
(3) When the speed of an object changes, its velocity also changes.
(4) When the velocity of an object changes, its speed may not change as the object can change direction without changing the speed to change its velocity. 

Other types of Speed

Average speed
= (total distance traveled)⁄(total time taken)

Instantaneous Speed: the gradient of the tangent at a point on the distance-time graph.

instantaneous speed = ∆d⁄∆t
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