Motion can be described in different ways, by using vector diagrams, by use of equations, or as we have seen by using distance versus time graphs. Understanding velocity versus time graphs adds another dimension to our understanding of motion. The interpretation of such graphs will see confusing at first. Sine we discussed distance versus time graph in such detail you will want t try to see the velocity graphs as similar to the distance graphs and will make the mistake of interpreting both graphs the same way. Key to understanding the velocity graphs is the fact that the velocity, not the distance or position, can be read off directly from the yaxis.
Let’s consider a car moving at a constant speed of 3 m/s for 10 seconds. Constant speed means that at every second the car is moving with the same speed. If you were to plot this kind of motion you would have to mark off 4 m/s at every, or every other second time interval.
Connecting the points leads to a straight line like it is shown on the right. Note that this line is horizontal and has therefore no slope. But unlike for a distance graph, zero slope does not mean that the object s not moving, it means instead that the object is moving at a constant speed. 
Another velocity graph would be the one shown at right. The slope of this graph is not zero but positive, which means that the velocity is increasing. Increasing velocity means nonuniform motion. It is now possible to calculate the slope by finding the ratio of the rise and the run. This ratio is the change in velocity for a certain time interval Dt, which is the definition for acceleration. A straight line means constant acceleration or a velocity that changes at equal rates.
