And finally, if a line crosses over the x-axis from the positive region to the negative region of the graph (or vice versa), then the object has changed directions. And one knows that an object is moving in the negative direction if the line is located in the negative region of the graph (whether it is sloping up or sloping down). So one knows an object is moving in the positive direction if the line is located in the positive region of the graph (whether it is sloping up or sloping down).

As learned in Lesson 1, a positive velocity means the object is moving in the positive direction and a negative velocity means the object is moving in the negative direction. 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. In the absence of air resistance The two balls end in a tie. A 1-pound ball and a 100-pound ball are dropped from a height of 10 feet at the same time. If the acceleration is negative, then the slope is negative (i.e., a downward sloping line). A moving object that is speeding up at a constant rate The slope at a point on a position-versus-time graph of an object is The objects velocity at that point. 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.

Slowing a velocity vector code