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Have you ever pushed a lawnmower up a steep hill? Depending on the size of the lawnmower, this might be hard work. The fact that you are pushing harder means that you have increased your energy input. There are various types of input and output energy that you will learn more about in this activity.

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Input energy means the amount of energy that enters into a system. Output energy means the amount of energy that leaves a system. When you put energy into something, you get an output (e.g., moving air from the fan or heat from the toaster).

However, the amount of energy that is produced for the specific task, which is known as output energy, is less than what is put in. How can that be? It is quite simple. Nothing on this planet is 100% efficient. This means that some energy is lost to the surroundings.

For example, let's say you ate a ham, cheese, lettuce, and mayonnaise bagel sandwich for lunch before you started to mow the lawn. It is easy to think that all the energy from the sandwich will go into helping you mow the lawn, but that is not true.

Where does the energy from the sandwich go? First, not all the food is digested. Some is eliminated from your body as waste. Second, a portion of the input energy in the remaining food is used for the body's cells. These cellular activities create heat. While some of the heat produced keeps your body warm, most of the heat is lost to the surrounding air. The harder you work, the more you sweat! The remainder of the sandwich energy is used to build your tissues such as muscle tissue.

Another way to look at input energy and output energy is an energy pyramid. An energy pyramid quantifies the amount of energy transferred from one level in a community to the next, when one organism eats another and where approximately 10% of the energy available is retained and passed along.

For example, if there are 1,000 kJ of energy available in a certain area, by the time the grass has used the energy necessary for it to survive, only about 100 kJ of energy is available to the mouse that eats the grass. After the mouse has used energy for its life functions, only about 10 kJ of energy is available to the coyote that eats the mouse. If a wolf were to eat the coyote, it would only receive about 1 kJ of energy.

The general rule for an energy pyramid is that 10% of the energy in a given level is available to the level above it.

Digging Deeper

Click on the Play button below to watch a video that explains the energy pyramid further.