Similarly, the velocity would be negative whenever the line lies in the negative region (below the x-axis) of the graph. Since the graph is a velocity-time graph, the velocity would be positive whenever the line lies in the positive region (above the x-axis) of the graph. The answers to these questions hinge on one's ability to read a graph.

Positive Velocity versus Negative Velocity But how can one tell whether the object is moving in the positive direction (i.e., positive velocity) or in the negative direction (i.e., negative velocity)? And how can one tell if the object is speeding up or slowing down? The slope of a velocity-time graph reveals information about an object's acceleration. This very principle can be extended to any conceivable motion. If the acceleration is negative, then the slope is negative (i.e., a downward sloping line). If the acceleration is positive, then the slope is positive (i.e., an upward sloping line). If the acceleration is zero, then the slope is zero (i.e., a horizontal line). The principle is that the slope of the line on a velocity-time graph reveals useful information about the acceleration of the object. time graphs for these two basic types of motion - constant velocity motion and accelerated motion (i.e., changing velocity) - reveal an important principle.

Velocity vs time graph