The law of energy conservation states that the total amount of energy contained within an isolated system will stay constant over time. In other words, the energy is conserved. As a consequence of this, energy can be neither created nor destroyed within a closed system. Instead, the only thing that can happen in such a system is that energy can change form — for example, chemical energy can transform into thermal energy. This law is an empirical law of physics.
The ancient philosophers — back to the time of Thales of Miletus — began to suspect the principles of conservation of which all is made. The pieces, however, were yet to be fully put together. Thales himself, for instance, did not identify what we know today as mass energy, believing it to be water.
The law of energy conservation is also linked also to Albert Einstein’s theory of relativity, which illustrates that energy and mass are one and the same and that one is not possible without the appearance of the other. As a result energy and mass are conserved separately in closed systems, and this principle was understood by the pre-relativistic physicists. Relativistic physics added an extra dimension by demonstrating that matter particles – such as those that make up atoms – were able to be converted to non-matter energy forms, such as kinetic energy or light. Relativists were able to show, however, that the conversion from matter to non-matter energy forms did not affect the total mass of systems, as the non-matter energy forms keep a constant mass through the process of conversion.
The modern definition of energy speaks of the conservation of a total energy system over time. This includes all forms of energy within the system, and also references the fact that all energy within the system is conserved over time for any single observer and all energy is the same value for all observers. As a result, in a closed, isolated system, despite the fact that matter and pure energy such as light and heat can be converted to one another the total amount of energy as well as the total amount of mass of isolated systems will stay constant over time as witnessed by any singe observer. If energy – in any form whatever – escapes from such isolated, closed systems the total mass of the system decreases in tandem with such a loss of energy.
One off-shoot of the law of energy conservation is that machines such as perpetual motion machines will only work as defined in the event that they deliver no energy whatever to their surroundings. If they output more energy than is input they will, by the law, lose mass and will disappear over the course of perpetual time, thus rendering them impossible. While many researchers have attempted to prove this wrong time and time again over the past few centuries the proof remains that perpetual motion is an impossibility due to the fact it goes against the natural law of energy conservation, making the quest a futile one.
(Energy FAQ Series)
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