What Is Energy? Definition and Types

What is energy? Definition and types

Energy is the ability of matter to produce work in the form of movement, light, heat, etc. It is a scalar physical quantity and can come in many forms.

It is a unique measure of various forms of movement and interaction of matter, a measure of the transition of matter from one form to another.

It is represented with different symbols:

  • Energy is represented by the symbol E.
  • The amount of heat uses the Q symbol.
  • The symbol W is used to designate the job.
  • For internal energy, U.

The electric field is the field generated by an electrically charged object. This field generates a force that acts on other objects also electrically charged.

Energy Conservation Law

The law of conservation of energy announces that: "energy is neither created nor destroyed", it can only be transformed. It is only possible to convert one type of energy into another type.

A closed system is a system that does not exchange energy with the outside. Therefore, in closed physical systems the total amount of energy always remains constant. 

For example, nuclear technology generates electricity from the force field of the nucleus of atoms. Types such as kinetic energy or chemical energy appear in the process.

In thermodynamics, it constitutes the first principle of thermodynamics (the first law of thermodynamics).

What Does It Mean That Energy Is Renewable or Non-renewable?

There are also two definitions of energy that refer to its origin. In this sense we can distinguish:

  • Renewable sources.
  • Non-renewable sources.

We usually refer to these two definitions to talk about the generation of electrical energy. However, these resources are often used to obtain heat.

Renewable energy is that which comes from inexhaustible sources. Some examples of these forms of energy are solar, energy and hydro, among others. They generally come from a natural resource. Solar radiation can be transformed into energy without being depleted.

The non- renewable energy source comes from limited sources. The consumption of resources is greater than its capacity for regeneration. Some examples are fossil fuels (coal, oil and natural gas) and nuclear reactors, among others.

Nuclear power plants can generate a large amount of energy. But uranium is a limited natural resource.

How Is It Used? Most Common Uses and Applications

The use of energy as a source of work has always been an essential need for man. It represents one of the fundamental factors of modern economic development and technical progress.

Until the beginning of the industrial revolution, man used as energy sources such as:

  • Muscle strength.
  • The force of the water.
  • The force of the wind for the production of mechanical work.
  • Vegetable fuels for obtaining heat. 

Until then these were the only resources used to obtain it. Over time they were refined to achieve higher yields. How they did it? More rational use of animals, improvement of sailing techniques, invention of the hydraulic wheel, etc.

Today, the most used resources are waterfalls, fossil fuels and nuclear fission. Less important are solar, wind, geothermal, and tidal energy.

Steam Engine and Thermal Engines

The beginning of development for energy exploitation techniques was in the appearance of the steam engine and the transformation of the hydraulic wheel into a turbine.

Later, the construction of the first combustion engines gave the definitive boost in the use of mechanical power from heat.

Fossil Fuels

The most important source is constituted by fossil fuels that have undergone exponential growth in recent years. The maximum performance is much lower than that obtained by hydraulic power, but its high energy concentration explains the considerable development it has undergone.

The heat obtained from fossil fuels is either used directly or converted into mechanical energy. For example in engines, turbines, etc. It is also used to obtain electricity.

Nuclear Energy

It is the third most used form of energy. Nuclear power is generally obtained by fission of nuclei of substances such as uranium, plutonium, thorium, etc.

The technology of nuclear fusion reactions is not yet sufficiently developed to allow industrial exploitation and is used only in experimental laboratories and warfare applications.

With nuclear fission it is obtained. It reaches much higher temperatures than those achieved with conventional fuels. However, the yields that can currently be obtained are still very low (of the order of 30%).

Nuclear technology is used above all in the production of electricity and in the propulsion of ships. The electricity obtained in a nuclear power plant has a reasonable cost only in the case of large reactors, which provide very high powers.


Energy is the ability to produce work, light, heat, etc. Its main characteristics are:

  • It is an essential element for life.
  • It can be presented in different forms and types: electricity, heat, etc.
  • It can be transformed.
  • Depending on whether it comes from inexhaustible resources, it can be renewable or non-renewable.

Published: December 10, 2009
Last review: May 14, 2020