Negative feedback is a reaction that causes a decrease in function. It occurs in response to some kind of stimulus. Often it causes the output of a system to be lessened; so, the feedback tends to stabilize the system. This can be referred to as homeostatis, as in biology, or equilibrium, as in mechanics. Negative feedback is also a reaction to an event or process, such as an evaluation of someone's work.
Biological Negative Feedback
Here are examples of biological negative feedback:
- Human body temperature - The hypothalamus of a human responds to temperature fluctuations and responds accordingly. If the temperature drops, the body shivers to bring up the temperature and if it is too warm, the body will sweat to cool down due to evaporation.
- Human blood pressure - When blood pressure increases, signals are sent to the brain from the blood vessels. Signals are sent to the heart from the brain and heart rate slows down, thus helping blood pressure to return to normal.
- When a human is hungry, metabolism slows down to conserve energy and allow the human to continue living with less food.
- Regulation of blood sugar in humans - When blood sugar rises, insulin sends a signal to the liver, muscles and other cells to store the excess glucose. Some is stored as body fat and other is stored as glycogen in the liver and muscles.
- Production of human red blood cells (erythropoiesis) - A decrease in oxygen is detected by the kidneys and they secrete erythropoietin. This hormone stimulates the production of red blood cells.
Mechanical Negative Feedback
Here are examples of mechanical negative feedback:
- The ballcock in a toilet rises as the water rises, and then it closes a valve that turns off the water.
- The fly-ball governor - This was used in controlling the speed of a steam engine. Two balls were attached to a frame and as their rotational speed increased, they swung outward and closed the inlet valve for steam. That caused the engine to slow down.
- Water flowing through a fracture in a rock will eventually deposit enough sediment to slow down the flow of the water.
- A thermostat senses the temperature and either turns the heater on or off.
- A spring can be compressed but will return to its original shape when pressure on it is released.
Negative Feedback in Nature
Here are examples of negative feedback in nature:
- The carbon cycle - The equilibrium of this cycle will change in accordance with carbon dioxide emissions.
- The photosynthesis in plants speeds up in response to increased levels of carbon dioxide.
- Carbonation - Rain and carbon dioxide combine with limestone to make calcium bicarbonate. This increases when the temperature lowers and is a factor in glacial weathering.
- Population of predators and prey - If the numbers of prey decreases, then some predators will starve, and their numbers will decrease.
- More radiation escapes into space from the upper atmosphere than from the lower portion. Global warming will reduce the rate of this escaping radiation and this will lessen the greenhouse effect.
Negative Feedback at Work
Examples of negative feedback at work:
- Being reprimanded for coming to work late
- Not being recommended for a raise after being rude to customers
- Getting a poor evaluation for not putting equipment away at closing
- Being written up for not getting a report completed on time
- A supervisor telling you that the choice of images in the presentation were in poor taste
Other examples of negative feedback include:
- A teacher marking a test to show the wrong answers
- A survey sent to consumers after making a purchase with places for negative feedback about the product
- An Army sergeant putting a private on report for being AWOL
- A coach explaining weaknesses in the team's defensive line
- Higher oil prices cause an increase in gas prices. Consequently, people drive less, so demand is decreased. This brings equilibrium to supply and demand.
Now you have seen all different kinds of negative feedback examples.