# What is the Principle of Conservation of Energy?

## What Does Principle of Conservation of Energy Mean

We explain what the Principle of Conservation of Energy is, how it works and some practical examples of this physical law.

## What is the Principle of Conservation of Energy?

The Principle of Conservation of Energy or Law of Conservation of Energy , 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 summarized in the principle that energy in the universe can neither be created nor destroyed , only transformed into other forms of energy, such as electrical energy into heat energy (this is how resistors operate) or into light energy (this is how they operate. bulbs). Hence, when performing certain jobs or in the presence of certain chemical reactions, the amount of initial and final energy will appear to have varied if its 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) done by said system . Thus, we have the formula: Q = .DELTA.u + W , from which it follows that Au = Q - W .

This principle also applies to the field of chemistry , since the energy involved in a chemical reaction will tend to always be conserved , like mass , except in cases where the latter is transformed into energy, as indicated by Albert's famous formula Einstein of E = mc 2 , where E is energy, m is mass, and c is the speed of light . This equation is of utmost importance in relativistic theories.

The energy, then, is not lost, as has already been said, but it can cease to be useful to carry out work, according to the Second Law of Thermodynamics : the entropy (disorder) of a system tends to increase as time passes , that is, 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 unchanged.

### Examples of the Principle of conservation of energy

Suppose there is a girl on a slide, at rest. Only a gravitational potential energy acts on it , therefore its kinetic energy is 0 J. When sliding down the slide, on the other hand, its speed increases and also its kinetic energy , but when losing height, its gravitational potential energy also decreases. Finally, it reaches maximum speed just at the end of the slide, with its maximum kinetic energy. But its height will have decreased and its gravitational potential energy will be 0 J. One energy is transformed into another, but the sum of both will always yield 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 electrical, thermal and light energy is the same, but it has been transformed from electric to light and thermal.

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