Interpreting velocity-time graphs

You should be able to draw and interpret the shape of a velocity-time graph for an object that is stationary, for an object moving in a straight line with constant speed and for an object moving in a straight line with steadily increasing or decreasing speed.

Velocity-time graph

In the graph, the object is stationary for the first 3 seconds, then has a steadily increasing speed for 2 seconds. For the next 3 seconds it has a constant speed, and for the last 2 seconds it has a steadily decreasing speed.

You can see that the speeds are changing steadily between 3 and 5 seconds and between 8 and 10 seconds, because the lines are not just going up and down, but are also straight.

One example of a velocity-time graph is a lorry tachograph. Tachograph records are circular disks recording the speed of the vehicle. This shows whether the lorry driver has been keeping to the speed limit and taking regular rest breaks.

A tachograph records the speed of the vehicle

This section of a tachograph disk shows that the driver started driving shortly after 9:30, and was travelling at 60 miles/hour until 10:50, when he took a 20-minute break. At 11:10 he speeded up again, and took a 10-minute break at about 12:00.