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# What is the principle of energy conservation?

We explain to you what the Principle of energy conservation is, how it acts and some practical examples of this physical law.

1. ### What is the principle of energy conservation?

The Energy Conservation Principle or Energy Conservation Law , also known as the First Principle of Thermodynamics, states that the total amount of energy in an isolated physical system (that is, without any interaction with other systems) will always remain the same, except when it is transformed into other types of energy.

This is summed up in the principle that energy cannot be created or destroyed in the universe , only transformed into other forms of energy, such as electrical energy in heat energy (thus resistors operate) or in light energy (thus they operate the light bulbs) Hence, when performing certain work or in the presence of certain chemical reactions, the amount of initial and final energy will appear to have varied, if their transformations are not taken into account.

According to the Principle of conservation of energy, when introducing a certain amount of heat (Q) into a system, it will always be equal to the difference between the increase in the amount of internal energy (ΔU) plus the work (W) performed by said system . In that way, we have the formula: Q = ΔU + W, from which it follows that ΔU = Q – W.

This principle also applies to the field of chemistry , since the energy involved in a chemical reaction will always be conserved , as is the mass , except in cases where the latter is transformed into energy, as Albert’s famous formula indicates. Einstein of E = mc 2 , where E is energy, m is mass and c the speed of light . With this formulation, relativity began and the creation of matter in the universe is explained.

Energy, then, is not lost, as has already been said, but it is degraded, according to the Second Law of Thermodynamics : the entropy (disorder) of a system tends to increase as time goes by . That is to say: systems inevitably tend to disorder.

The action of this second law, in accordance with the first, is what prevents the existence of isolated systems that keep their energy intact forever (such as perpetual motion , or the hot contents of a thermos). That energy cannot be created or destroyed does not mean that it remains immutable.

1. ### Examples of the principle of energy conservation

Suppose there is a girl on a slide, at rest. Only a gravitational potential energy acts on it , so its kinetic energy is 0 J. When the slide slides down, on the other hand, its velocity increases and its kinetic energy increases , but when it loses height its gravitational potential energy also decreases. Finally, it reaches the maximum speed just at the end of the slide, that is, its maximum kinetic energy, but its height will have decreased and its gravitational potential energy will be 0 J. There is how one energy transforms into another, but the sum of both will always throw the same amount in the system described.

Another possible example is the operation of a light bulb, which receives a certain amount of electrical energy when the switch is operated, and transforms it into light energy and thermal energy, as the light bulb heats up. The total amount of electric, thermal and light energy is the same, but it has been transformed from the first into the second two.

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