Hopefully you have now noticed these two relationships
Graphs H and I form the two "halves" of a parabola that opens upward. They represent situations in which the acceleration is positive.
Graphs J and K form the two "halves" of a parabola that opens downward. They represent situations in which the
acceleration is negative
.
Remember that acceleration can be calculated as the slope of a velocitytime graph. The velocity graphs that correspond to Graphs H and I have positive slopes. While those corresponding to J and K have negative slopes.
Whenever an object is losing speed, its velocity graph moves towards the xaxis (where velocity = zero). When it is gaining speed, its velocity graph moves away from the xaxis to values on the yaxis that represent "greater" speeds.
