1. Understanding and interpreting graphs
Speed Time Graphs
Understanding and interpreting graphs

2. The Graphs ‘show’ us certain information about the Speed
Just like distance/time graphs, there are some basic graphs to learn. The first is just a horizontal line:
Time always runs horizontally (the x-axis). The arrow shows the direction of time. The further to the right, the longer time from the start.
Velocity runs vertically (the y-axis). The higher up the graph we go, the faster we are travelling.
Don't be tempted to think this means it's stationary(standing still)! This is speed/time, and the speed is both positive and constant. This shows a constant speed.

3. How about this one, can you explain what is going on here?
When you try to understand a graph just ask yourself “as time goes by what is happening to the speed?”
In this graph the speed is increasing, so the object must be accelerating.

4. And how about this one?
The speed is decreasing, so the object must be slowing down.

5. What about comparing two lines at once?
Both the yellow and blue line show increasing speed.
They both reach the same top speed, but the blue one takes longer.

6. Speed Time Graphs: Distance
Speed-Time graphs can be used to find out how far something has travelled. In the example below, a speed of 30 m/s is maintained for 20 seconds:
One way of calculating the distance is to use distance = speed × time. This gives:
distance = 30 × 20 = 600 m

7. Another way to calculate distance:
An alternative way of finding the distance travelled is simply to calculate the area under the line.
In this case: distance = 30 × 20 = 600 m. Which is precisely the same calculation as before!

8. These types of graphs are a little harder to undertasnd
Things often change speed, so speed-time graphs can be more complicated:
The average speed can be used to find the distance travelled:
Average speed = ( ) / 2 = 20 m/s Distance = average speed × time Distance = 20 × 20 = 400 m
Alternatively, the area may be found underneath the line:
Blue rectangle = 20 × 10 = 200 m White triangle = (20 × 20) / 2 = 200 m Total distance = = 400 m Both methods give the same result, as we should expect! Use whichever you find easiest.

9. Speed Time Worksheet
Interpret the graphs and create an explanation of what is going on.