Why do scientists track the energy in a system?

The supply of energy and of each needed chemical element restricts a system operation -- for example , without inputs of energy ( sunlight ) and matter ( carbon dioxide and water ) , a plant cannot grow. Hence , it is very informative to track the transfers of matter and energy within , into , or out of any system under study.

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the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.