The shape of a velocity-time graph reveals much information about the motion of an object. Whether the line is horizontal or sloped and where the line is located reveals information about the manner in which the object is moving. Learn more in the How to Think About This Situation section. 
 

There are four velocity-time graphs. You must choose any which is /are representative of an object that is moving in the + direction and also speeding up. The way to think about these graphs is described below.

Velocity-Time Graphs: A sloped line (whether straight or curved) is an indication of a changing velocity motion. A line in the + region of the v-t graph is an indication that the object is moving in the positive (rightward) direction. And a line in the - region of the v-t graph is an indication that the object is moving in the negative (leftward) direction.  Lines that are heading away from the time axis represent speeding up motions. And lines that are approaching the time axis represent slowing down motions. 

Don't Be Confused: The term "speeding up" can be confusing for many students. It is the "up" part of speeding up that leads to confusion. It is one reason than we combine the term with the equivalent expression "getting faster". To be speeding up means that the speed is increasing towards larger values. The confusion becomes a problem when students get pre-occupied with "up"; they then tend to pick lines that are sloping upwards. But don't be confused! Getting faster or increasing speed means that the lines will be heading away from the time axis. 

This Too Can Be Confusing: All the graphs in this Concept Builder are velocity-time graphs. But many students have also studied position-time graphs. These two graph types have different rules and you will have to keep them straight in your head. For a position-time graph, a speeding up motion is described by a line that curves and becomes steeper over the course of time. You will see two of those lines as options. But don't be fooled! The rule for speeding up (and for moving in the + direction) is different for velocity-time graphs. You can read the rule in the Velocity-Time Graphs section above.