A horizontal line means the object is moving at a constant speed. The gradient of the line = the rate of change of speed. The steeper the line, the greater the increase in speed. The area under the ...

The graph above is for an object which is thrown vertically upwards with an initial velocity of 20 m/s. In the time period 0-2 seconds – the object decelerates from 20 m/s to 0 m/s.