What is the difference between velocity and speed? Velocity is the vector equivalent of speed. Since speed is the distance travelled per unit time, this means that velocity is displacement travelled per unit time.
If you're estimating how long a journey will take, you will probably use an average velocity. However, sometimes instantaneous velocity is more important.
Key Concepts
Velocity is defined as the rate of change of displacement:
\(v={\Delta s \over \Delta t}\)
The derived SI unit of velocity is m s-1.
Speed is defined as the rate of change of distance:
\(\text {speed} = {\text {distance} \over \text {time}}\)
Speed is a scalar and velocity is a vector. This means if you tavel in a complete circle at constant speed your velocity is constantly changing and your average velocity will be zero.
Watch this clip and notice the changing direction of the velocity arrow.
Any moving object has an instantaneous velocity.
Instantaneous velocity is the velocity you would calculate if you divided motion into small steps and calculated the step length divided by time taken: \(v_{\textrm {instantaneous}}={\delta s \over \delta t}\).
The direction of the velocity is the same as the direction of the change in displacement.
How much of Velocity and speed have you understood?