Distance-Time Graphs

A distance-time graph is exactly that - a graph which plots the distance compared to time. An example graph is given below for a person walking down a street...

A diagonal line on the graph shows that the distance is increasing at a steady rate (they are travelling at a constant speed) - lines A and C show this. A horizontal line shows that the person has stopped moving (the distance is not increasing) - line B shows this. We can compare the difference between two speeds by the lines on the graph - the person is travelling at a faster speed in part C than in part A because the line for part C is steeper.

We can also use the graph to calculate the speed of the person by using the equation...

In Part A the speed can be calculated by knowing that the distance travelled was 10m and the time taken was 25seconds - so the speed is 10÷25 which gives a speed of 0.4 m/s.

In part C the Distance is 20m (the person started part C of the journey at 10m and finished it at 30m) and it took 25 seconds (they started at 35 seconds and finished at 60 seconds), so the speed would be 20÷25 which gives a speed of 0.8m/s

We can also calculate the average speed of the journey by dividing the total distance by the total time. In this case the total distance is 30m and the total time is 60 seconds so the average speed was 30÷60 = 0.5m/s.

A downwards line on a distance-time graph indicates the object is moving backwards.

For more information on distance/time graphs watch the video below...

 

Or click on the picture below for more information about distance-time graphs from the Science Year website...