year 8 maths

9C
Line graphs
539
9C Line graphs
A line graph is a connected set of points joined with straight line segments. The variables on both axes
should be continuous numerical data. It is often used when a measurement varies over time, in which
case time is conventionally listed on the horizontal axis. One advantage of a line graph over a series of
disconnected points is that it can often be used to estimate values that are unknown.
Let’s start: Room temperature
As an experiment, the temperature in two rooms is measured hourly over a period of time. The results are
graphed below.
Room B
Room A
35
30
30
25
25
20
20
15
15
10
10
5
5
Temperature (°C)
0 1 2 3 4
Time (hours)
Temperature (°C)
0 1 2 3 4
Time (hours)
• Each room has a heater and an air conditioner to control the temperature. At what point do you think
these were switched on and off in each room?
• For each room, what is the approximate temperature 90 minutes after the start of the experiment?
• What is the proportion of time that room A is hotter than room B?
■ A line graph consists of a series of points joined by straight line segments. The variables on
both axes should be continuous numerical data.
■ Time is often shown on the horizontal axis:
Mass
Key ideas
Time
■ A common type of line graph is the
distance–time graph studied in Chapter 5.
This type of graph is commonly referred
to as a travel graph.
• Time is shown on the horizontal axis.
• Distance is shown on the vertical axis .
• The slope or gradient of the line indicates
the rate at which the distance is changing
over time. This is called speed .
Distance (km)
60
50
40
30
20
10
0
At rest
30 km in 1 hour
(30 km/h)
1 2 3 4 5 6
Time (hours)
30 km in 3 hours
or 10 km/h
Cambridge Maths NSW
Stage 4 Year 8 Second edition
ISBN 978-1-108-46627-1 © Palmer et al. 2018
Cambridge University Press
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