Water found at the top of a possesses potential energy. As it passes into the waterfall, that potential energy is converted into kinetic energy. More precisely, pulls things towards the and the water found at the top of waterfall – unable to pass through the underlying – is trapped some distance from ís center. Once that rock is removed, which occurs at the of the waterfall, then the water is able to get a bit closer to the center the Earth, which it accomplishes by tumbling down as part of the waterfall. Gravity accelerates the water as it falls, converting what was potential energy into what is now kinetic energy, that is, the energy of motion.
represent energy lows. That is, they are an easily acquired state, of a system, and one from which energy is not easily extracted. In yet other words, systems at equilibrium possess no easily extracted energy. Pushing a system away from equilibrium consequently requires energy, and does so for the same reason that carrying a of water back to the top of a requires an input of energy. That input of energy is equivalent to converting kinetic energy into potential energy. Thus, pushing a system away from equilibrium too is equivalent to converting kinetic energy into potential energy.
Once a system has been perturbed away from , then its tendency will be to fall back towards equilibrium. This falling back towards equilibrium can be thought of as kinetic energy. Similarly, if the system can be trapped away from equilibrium, then the trapping is the equivalent of storing potential energy. Once those traps or are released, however, then the potential energy will be converted into kinetic energy, and the system will thus fall towards equilibrium. At the point of equilibrium both potential energy and usable kinetic energy are no longer present.
When looking at systems – any kind of system, not just biological ones – it can be useful to think about how the system can "move" so that it possesses less energy, e.g., a at the top of a has more energy associated with it then a rock that is found at the bottom of a cliff. Will the rock at the bottom of the cliff move to the top of the cliff? Not very likely, but why not? The answer is that the system, the rock and its surroundings, will tend to lack the energy necessary to move the rock from the bottom to the top of the cliff. On the other hand, the rock at the top of the cliff already possesses all of the energy necessary to move it from the top of the cliff to the bottom, and we know this is so because our experience is consistent with heavier-than-air objects falling downward rather than "falling" upward. That is, we understand that rocks found at the tops of cliffs possess more energy than those found at the bottoms of cliffs, and this is true even if we haven't necessarily ever thought about these situations explicitly in terms of energy.
Where does all the energy that has been lost from a system go once movement from higher energy to lower energy states has occurred? The answer is that this energy can be put into other systems, such as the generation of using means, but ultimately the energy within as systems may instead be converted into what is known as waste heat, a form of energy that organisms are unable to harness except for the sake of warming their bodies. The at the top of the possesses more energy, more potential energy, than the rock found at the bottom of the cliff. Upon moving from the top of the cliff to the bottom of the cliff that potential energy is converted first to kinetic energy and then to waste heat.