Principle of conservation of energy

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

1. What is the Principle of energy conservation?

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) it 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 energy. Caloric (thus operating the resistors) or in light energy (thus operating the bulbs). Hence, when performing certain work or in the presence of certain chemical reactions, the amount of initial and final energy seems to have varied, if its transformations are not taken into account.

According to the Principle of conservation of energy, when introducing into a system a certain amount of heat (Q), this will always be equal to the difference between the increase in the amount of energy Internal ( U) plus the work (W) performed by said system. In that way, we have the formula: Q = U + W, from which it follows that U = 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 in which the latter is transformed into energy, as indicated by the famous Albert Einstein formula 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.

See also: Law of Conservation of Matter.

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, therefore its kinetic energy is 0 J. When the slide slides down, on the other hand, its speed increases and its kinetic energy increases, but when its gravitational potential energy decreases its height 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 is transformed 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.