Velocity and speed are often confused, but they are very different.
We define the average speed as the distance traveled divided by the time it takes to travel it. Distance is step size times the number of steps, irregardless of direction. Speed is a scalar value and is always positive or zero.
Average Speed = distance / time
Average velocity is defined as the displacement divided by time. Displacement measures where you end up relative to where you started. Velocity is a vector value. It has magnitude and direction.
Average Velocity = displacement / time
Even if you travel a great distance but return to your starting point, then your displacement is zero and your average velocity is zero.
Slide the green/red controls in the interactive diagram above to compare speed and velocity for different time spans over the time/position curve.
Subject Index for all interactive diagrams
interactagram.com - Physics - Kinamatics - Position, Velocity, and Acceleration - Speed vs Velocity
Source Flash: speedVsVelocity.zip
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