Feedback Loops: Understanding Why Things Change or Stay the Same

Tracing closed loops of cause and effect help us to understand how change occurs in dynamic systems. When the change in a system feeds back to cause even more change in the system, this pattern is known as reinforcing feedback. When reinforcing feedback is present, a relatively small change in one part can eventually lead to a much larger change in another part. Reinforcing feedback loops act as engines of growth or decline: think of your saving account (if you actually save and don't spend), or the spread of a rumor.

In other systems (or even in parts of the same system), things tend to come back more or less to their original state or close to equilibrium over time By its very nature, this type of feedback loop, known as balancing feedback, can help keep a system healthy, or close to its optimum or desired functioning: think of homeostasis, predator/prey, or supply and demand.

Watch the videos below to see if you can identify feedback loops at work, and describe each in the text box below. Is each loop you've identified reinforcing or balancing? The essays that accompany the videos on PBS LearningMedia explain their feedback loops in greater detail.