Here we explain the difference between distance and displacement, vector and scalar quantities as well as speed and velocity in sport and how to do calculations.

## Distance and displacement?

What is the difference between distance and displacement? Displacement is how far a body has moved. It is the shortest distance between the starting point and the finishing point. For example, a sailing Yacht might zig-zag (tack) backward and forward in order to sail 100m East. The displacement of the Yacht is 100m.

However, the distance the Yacht has covered is more than 100m because it has had to zig-zag through a longer path. Both distance and displacement are measured in metres (m).

More examples of distance and displacement:

• A marathon runner has run a distance of approximately 26 miles 385 yards. Is displacement the same? Probably not unless the course is one very straight line.
• A 400m sprinter? The distance travelled by the sprinter is 400m, but the displacement is practically zero as they finish in the same place they started.

## Speed and velocity

Speed and velocity are used to describe how fast something is going. Speed is the rate of change of distance.

Speed (m/s) = Distance (m) / Time (s)

Velocity is the speed of a body in a specific direction and is the rate of change of displacement. Velocity is what is known as a vector quantity which means it needs a direction and well as a magnitude. So if the direction of the moving body changes then the velocity changes even though the speed might stay the same.

Velocity (m/s) = Displacement (m) / Time (s)