This is a basic physics tutorial that is targeted at GCSE (grade 9 and grade 10) standard explaining distance-time graphs, and their role in calculations.
In our last tutorial we learned that the average speed of an object can be calculated by dividing the distance traveled by the time it took to travel that distance:
average speed = distance / time
What are distance-time graphs?
Distance-time graphs are a way of representing a journey in a graph, typically with the y-axis representing distance, and the x-axis representing time.
Calculate average speed from a distance-time graph
Importantly the gradient or slope of a conventional distance-time graph (y-axis = distance, x-axis = time) is the same as average speed:
Hover your mouse over the graph below to see how to work out the average speed of the represented journey.
If the axes were swapped, then you would need to take the inverse of the slope to calculate speed. Below is an example of a time-distance graph for you to practice with. If you're not sure what to do, hover your mouse over the graph for two different methods to calculate the average speed of the represented journey.
Method 1 involves reading values off the graph for distance traveled and time taken; method 2 involves calculating the slope and then inversing it to get the average speed.
What is the benefit of a distance-time graph?
Distance-time graphs are particularly useful because they make it easy to compare one journey to another at a glance i.e. without having to do any calculations. Knowing what you know now, look at the below graph and work out which of the three lines depicted represents the journey with the fastest and slowest average speed; then mouse over the image for the answer.
Some more examples
In the above video we take a look at four different journeys represented on a distance-time graph and practise calculating their respective average speeds. Furthermore, there is a complementary free worksheet below for you to work through in your own time to consolidate your understanding. It includes worked through answers for you to check your work against.