Reading travel graphs
A travel graph shows the distance travelled away from a set point against the time. This allows us to identify the speed at which they have travelled, points at which they were stationary (not moving), and when they are returning to the starting point.
It is important to be able to identify the following types of movement on a distance time graph:
As the distance is not changing, the horizontal line indicates a stationary period.
A straight line shows that the object is moving with a constant speed. Looking at the graph we can see that the green line is steeper than the red line. This means that the speed is greater.
We can calculate the speed using the formula:
\(\text {speed = distance ÷ time}\)
This curved line starts off steep and the slope becomes more gradual. This indicates deceleration.
This curved line is getting steeper as time increases. This indicates acceleration.
Example
This distance time graph shows a person’s journey. We can look at each part of the graph individually to work out what is being shown.
Question
1. What is happening in the section of the journey marked A?
2. What can you say about section B of the journey?
3. What speed is the person travelling at in section C?
4. Describe what is happening at section D.
5. What speed is the person travelling at in the last part of the journey, section E?
1. The first part of the journey starts at 8:00 and finishes at 9:00, lasting an hour.
Miles away from home begins with 0 (at home) and finishes at 3 miles.
\(\text {speed = distance ÷ time}\)
= 3 miles ÷ 1 hour = 3 miles per hour
2. They stopped for 30 minutes (0.5 hours) between 9:00 and 9:30.
3. The next section of movement is from 9:30 to 11:00, which is 1 hour 30 minutes.
To use this time in speed calculations it must be in hours only so we use 1.5 hours.
This section goes from 3 miles to 8 miles on the graph indicating a distance of 8 – 3 = 5 miles.
\(\text {speed = distance ÷ time}\)
= 5 miles ÷ 1.5 hours = 3.33 miles per hour (to two decimal places)
4. The part of the graph marked D shows that they stopped for one hour.
5. \(\text {speed = distance ÷ time}\)
= 8 miles ÷ 1 hour = 8 miles per hour
Question
What distance is travelled overall?
16 miles: 8 miles there and 8 miles back.
