Telling the story of a graph

0:00This graph shows one trip from home. What story does it tell?

0:06The horizontal axis shows time in minutes. The vertical axis shows distance from home in metres.

0:14Each point pairs a time with a distance: after 10 minutes, the person is 600 metres from home.

0:21A common mistake is to see a picture of the path, like a hill. It is not a hill: it is distance from home against time.

0:30Match three short stories to the three parts: runs home, walks to a friend's house, stays there for 20 minutes.

0:39First the line rises: the distance from home grows steadily. That is the walk to the friend's house.

0:47Then it is flat: the distance stays at 900 metres while time passes, so the person is not moving. That is the stay.

0:58Last, it falls back to 0 metres: the person comes back home. That is the run home.

1:07How steep a part is shows the speed: speed equals distance divided by time.

1:14The walk covers 900 metres in 15 minutes. 900 divided by 15 is 60 metres per minute.

1:23The stay lasts from 15 to 35 minutes: 35 minus 15 is 20, just as the story says. 0 metres in 20 minutes is a speed of 0.

1:35The run takes 40 minus 35, just 5 minutes, for the same 900 metres. 900 divided by 5 is 180 metres per minute.

1:46180 divided by 60 is 3, so the run is 3 times as fast as the walk, and its line is 3 times as steep.

1:57Up means moving away, flat means stopped, down means coming back, and steeper means faster.