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Thermodynamics.
Transformation of energy

Thermal energy and combustion.
Effects of thermodynamics

Entropy

Examples Of The First Law Of Thermodynamics

Examples of the first law of thermodynamics

The first law of thermodynamics states that: "The total energy of an isolated system is neither created nor destroyed, it remains constant".

Although the definition seems very technical and difficult to understand, there are numerous everyday examples that apply this thermodynamic principle.

We will use three examples:

  • A boy who throws a ball in the air.

  • Steam machines.

  • Solar energy.

Heat, energy and work, according to the international system of units is measured in Joules.

Conservation of energy in a balloon thrown into the air

Two types of energy are involved in this example: kinetic and potential.

  1. A boy throws a ball into the air.

  2. The moment the ball leaves your hands it has speed, therefore it has kinetic energy. It has not yet gained height, therefore it has no potential energy.

  3. As he climbs he loses speed and gains height. It loses kinetic energy and gains potential energy.

  4. When it reaches the highest point, it only has potential energy.

  5. Finally it goes down again and the energies are reversed again.

Steam machines

The development of the steam engine involved the start of development of the first of the laws of thermodynamics.

This is the first time that a thermodynamic transformation has occurred to convert thermal energy into mechanical energy. Its operation is based on the variation of the pressure-volume ratio.

Examples of the first law of thermodynamicsLet's analyze how energy is transformed into a steam locomotive. We consider the locomotive as a thermodynamic system.

  1. Initially all the internal energy of the system is internal energy of the fuel. Charcoal.

  2. When combustion there is a change in energy, it is transformed into thermal energy.

  3. All of this amount of heat is used to generate steam and power the engine's pistons. At this time, it is converted into mechanical energy.

  4. When the engine moves, the locomotive moves. Get a speed. We now have kinetic energy.

In our example the locomotive is not an isolated system. Therefore there is heat exchange with the outside. In a steam locomotive there are many losses for example:

  • The smoke from combustion and the hot steam that escapes.

  • The friction between the different mechanisms generates negative work.

  • Friction with the tracks.

  • Friction with air.

  • The heat from the boiler that is transmitted to the air.

Conservation of energy in solar energy

An example of this principle is solar energy. It is applied both in photovoltaic and in solar thermal.

The atoms of the particles that make up the Sun contain energy. Internal energy. These atoms constantly undergo a nuclear reaction. Nuclear fusion converts this chemical energy into radiation.

The solar radiation that reaches Earth is captured by solar panels.

Solar panels transform this energy into electrical energy ( photovoltaic energy) or heat energy (thermal energy).

So why is the performance of a solar panel not 100%?

All the solar energy that reaches the solar panel is transformed. But it is not all transformed into the same type of energy. Part of the radiation received by a photovoltaic module is converted into electricity.

However, another part is converted to heat, heating the panel; or it bounces back into the atmosphere.

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Published: June 4, 2020
Last review: June 4, 2020