11.5 Real-life and distance-time graphs — Learn
Prerequisites: read graph axes and calculate with units.
Objectives
By the end of this section, you can interpret real-life graphs and use gradient as a rate of change, including speed on a distance-time graph.
Read a real-life graph
A graph connects two quantities. Read the axis labels and units before interpreting it. On a distance-time graph, time is usually horizontal and distance is vertical. The gradient is change in distance divided by change in time, so it gives speed. A horizontal section means the distance is unchanged.
Worked example. A cyclist travels 18 km in 1.5 hours. Find the constant speed.
Kilometres divided by hours gives kilometres per hour.
Watch out. Convert time units before dividing. For example, 30 minutes is 0.5 hours, not 30 hours.
Progress check
The walker covers 2 km in 0.5 hours, so the speed is km/h. In one hour, the walker is 4 km from home.
You should now be able to
- interpret real-life graphs and use gradient as a rate of change, including speed on a distance-time graph.;
- check your result by substitution or by interpreting the graph;
- explain the method in your own words.