Also shown is an estimate of future world population which is close to the mid-range United Nation Environmental Program (UNEP) best guess for future population to stress that exponential growth is not realistic for world population although it works fairly well for the time between 19.
After you eat something, your body absorbs the glucose from your bloodstream and deposits it into your blood. The main sugar found in your blood is glucose. In the graph below we show the world population predicted for a fixed 2% growth rate from 1950 to 2050. Examples of Negative Feedback Regulating Blood Sugar Every time you eat, a negative feedback mechanism controls the level of sugar in your blood. Not all positive feedbacks give exponential growth but all, left unchecked, will result in unlimited (or unstable) growth. The solution to this is P(t)=Po(exp) or exponential growth. This idea can be modeled nicely with the differential equation dP/dt=+rP, where P is population and r is the percent birth rate. In the figure below connecting population to births, large populations cause large numbers of births and large numbers of births result in larger population. Positive feedbacks will result in unlimited growth (until checked) and are sometimes referred to as vicious cycles. This same trick of multiplying the signs of the connections around a loop together to find out whether it is a positive or negative feedback loop works for more complicated loop structures with many more connections.Īn example of positive feedback is world population with a fixed percentage birth rate. Going around the loop the positive connection times the negative connection gives a negative loop feedback effect. When these two connections are combined we get a negative feedback loop as shown at left in which the coffee temperature approaches the stable equilibrium of the room temperature.