How To: Calculate Average Linear Velocity Or Speed

In 2A1 Mechanics we really just deal with the vector quantity velocity instead of the scalar quantity speed. However, it’s important to realize that velocity and speed are different. Speed is simply not the velocity without direction.

If you are unsure what vector and scalar quantities are, check out this Khan Academy video: Introduction to Vectors and Scalars

Remember that velocity being a vector quantity has magnitude and displacement. Speed being a scalar quantity only has magnitude and no direction.

This means when describing the vector quantity velocity of your vehicle you would say 100km/hr “magnitude” to the north “direction”. The direction can be any direction up, down, north, east, west, south, a positive or negative sign in front. What’s important being a vector quantity is that it has magnitude and direction.

When describing the scalar quantity speed of your vehicle you would say 100km/hr. Only the magnitude of the vehicle is given, no direction of movement is provided.

Definitions

Average Velocity: The change in position “displacement” over the change in time. Remember that displacement has magnitude and direction.

Average Speed: Distance travelled over time. Remember that distance has magnitude only and no direction.

Average Velocity Or Speed Formulas

Velocity

The formula to determine average velocity:

Another way to think about it:

The formula for average velocity when an object increases from an initial velocity to a final velocity can be determined with the formula below:

Speed

Note: Speed uses distance, not displacement. Displacement has both magnitude and direction. Distance has only magnitude and no direction.

Formula Variables

s = displacement (m)

t = time (s)

u = initial velocity (m/s)

v = final velocity (m/s)

d = distance (m)