Displacement and velocity - Higher

The only difference between velocity and speed is that velocity has a direction, and so is a vector quantity.

Average velocity = \frac{\text{displacement}}{\text{time}}

Displacement is the distance moved in a straight line, in a given direction, from the starting point.

Displacement is a vector quantity as it has size and direction.

Illustration showing the difference between distance and displacement
Question

If a car travels 24 m east in 3 seconds, what is its velocity?

Displacement = 24 m east.

Velocity = displacement ÷ time.

Velocity = 24 m ÷ 3 s = 8 m/s east.

The velocity of the car is 8 m/s east.

Question
An aerial view of the floorplan of a house. The house is square, and each side measures 10 metres. The upper right corner is labelled 'Start/Finish'.

You walk all the way around the house in the diagram in 20 seconds.

a) What is your speed?

b) What is your velocity?

a) speed = distance moved ÷ time taken

distance moved = 10 m + 10 m + 10 m + 10 m = 40 m.

Speed = 40 m ÷ 20 s = 2 m/s.

Your speed is 2 m/s.

b) Velocity = displacement ÷ time

displacememt = 0 (Your displacement is nothing. You have ended up at your original position. No net distance in a straight line has been made between the start and end point.)

velocity = 0 m ÷ 20 s = 0 m/s.

Your velocity is zero.