Line graphs

Philip and Kim will each plant a sunflower. They are having a sunflower competition! Whoever has the longest sunflower after 90 days, wins. Every ten days they will measure the height of the sunflowers and write down the result. Kim and Philip put the sunflower seeds in the soil.

The competition begins! The days pass... After ten days, nothing is visible but soil… But after 20 days, both plants are visible. They measure. Kim’s sunflower is four centimetres high, and Philip’s is eight centimetres.

Philip is leading! They write down the results in a table. They also want to describe how the sunflowers grow – with a graph. On the horizontal axis of the graph, they write the time, in days. They put the last day, day 90, at the far right of the axis.

Then they mark on the axis, 10, 20, 30, all the way up to 90 days, with equal distance between the markings. They write days on the far right. Then, the vertical axis. On that axis they show the height of the sunflowers. The height changes with time.

They measure in the unit centimetres and write it at the top on the axis. They do not think the sunflowers will be higher than 200 centimetres —so they set the highest value to that. Then they mark every 20 centimetres, up to 200. It is the same distance between the markings. So after 20 days Kim’s sunflower is four centimetres high and Philip’s eight centimetres.

Now they mark it on the graph. First they look along the horizontal axis until they reach 20 days. Just above 20 days, they should make two points, for the height of the plants. To find four and eight centimetres, they use the vertical axis. They make one mark above 20 days, at a height of four centimetres, and another, at a height of eight.

To show which point belongs to whom, they make Kim’s point blue, and Philip’s green. Another 10 days pass. It is now 30 days since they planted the sunflowers. Kim’s sunflower is 20 centimetres, but Philip’s is still a little bit taller. It is 25 centimetres.

On the horizontal axis they are now at 30 days and on the vertical axis at 20 and 25 centimetres. They draw two points above 30 days at heights of 20 and 25. 40 days: Now Kim’s sunflower has grown again. It is 36 centimetres while Philip’s is just 30 centimetres. At 40 days: one point at 36 centimetres, and one at 30.

The small points are not very visible. Therefore, they link the points together with straight lines. Kim’s points with blue lines, and Philip’s with green. A graph where you mark different values and connect the markings with straight lines, is called a line graph. The competition continues… Kim and Philip continue to care for their sunflowers by watering and fertilizing.

50 days after planting, Kim’s sunflower is 47 centimetres and Philip’s is 50 centimetres. Now Philip’s sunflower is taller again. They mark two new points and draw lines from the previous points. Then they do the same after 60 days... ...70 days ...and 80 days. Now the exciting part.

Day 90. Who is winning? Kim’s sunflower is 169 centimetres, and Philip’s is... 185 centimetres! Philip won the sunflower competition.

And we got a line graph. Philip’s sunflower gets a gold medal. Kim: Now mine is the tallest. It should get the medal. Philip: Okay.

Kim: Now yours is the tallest again. Philip: I won – again!