Final answer:
A line graph is used to visually represent the behavior or values of two variables over time, such as the unemployment rate or the speed of an object during a trip.
Step-by-step explanation:
A line graph is a visual representation of the occurrence of a behavior over time. It is one of the most effective formats for illustrating a relationship between two variables, especially when they are both changing. For instance, in studying the unemployment rate over a period of time, a line graph can clearly show any upwards or downwards trends. In physics, these could be position-time graphs, velocity-time graphs, or speed-time graphs which are significantly useful in visualizing the motion of an object over time. For example, these types of graphs can simplify and represent the motion during a trip to the store, assuming constant speed and a straight path for the sake of the model.
Additionally, another application is the use of graphs for visualizing the transduction of a signal along a signaling pathway, or in a psychology context, sticker charts used as a behavior modification tool are also a form of visual representation of behavior over time.