The average velocity tells how fast an object is moving over time and is defined as the total displacement between two points divided by the time taken to travel between them. For example, if p1 and p2 are the positions of an object at time t1 and t2, then average x-velocity is given as Δx divided by Δt. Note that the average velocity is a vector quantity and could be positive or negative depending on whether the displacement is positive or negative. The position versus time graph is a pictorial way to represent how an object changes position with time. It plots the time on the x-axis and the position on the y-axis. Therefore, the average x velocity of the object equals the slope of the line p1, p2. Average speed is defined as the total distance traveled by a body divided by the time taken to complete the distance. Unlike average velocity, it is a scalar quantity.