USING GRAPHS

It is often a lot easier to describe how an object is travelling by drawing a graph of its motion. The example below shows how the velocity of a girl travelling in a car might change on part of her way to school.

We can describe the motion of the car in the three different parts of the journey:
(a) O to A - the velocity increases steadily from 0 m/s to 20 m/s in 10 seconds.
(b) A to B - the velocity stays the same at 20 m/s for the next 30s
(c) B to C - the velocity decreases to 0 m/s in 20s.

Using: distance = average velocity x time
Distance travelled AB = 10 x 10 = 100m
Distance travelled AB = 20 x 30 = 600m
Distance travelled BC = 10 x 20 = 200m

Total distance travelled OC = 900m

But this is the AREA under the line.

This is always true no matter how the object moves.