Speed Time Graph

A speed time graph is a graph that shows the motion of an object against time.

They can also be referred to as velocity-time graphs.

The units of speed used for a speed-time graph can vary, but the most common are kilometres per hour (km/h), metres per second (m/s) and miles per hour (mph).

E.g.

This speed-time graph shows the speed of an object in metres per second over a 10 second period.

The object accelerated from rest at a constant rate for 4 seconds until it reached a speed of 10 m/s. It then remained travelling at 10 m/s for a further 5 seconds before then decelerating to rest in 1 second. (Decelerating is when an object slows down.)

The straight line numbered f{1} shows a constant acceleration. This acceleration can be calculated by finding the gradient of the line.

Acceleration is the rate of change in speed over time. Here is the formula

The horizontal line numbered f{2} shows the object moving at a constant speed.

The straight line numbered f{3} has a negative gradient, therefore, shows a deceleration (the object is slowing down).

The total distance the object has moved can be found by calculating the area under the speed-time graph.

The average speed can be calculated by dividing the total distance travelled by the total time taken.