What Is the Best Definition of Energy?

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

What is the best definition of energy?

Therefore, the energy definition in physics is: “The capacity of a physical system to do work.”

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

How Is It Represented?

The concept of energy can be represented with different symbols:

  • In general terms, energy is represented by the symbol E.

  • The amount of heat uses the symbol Q.

  • The symbol W is used to designate work.

  • The internal energy is represented by the letter U.

In all cases, the unit of energy in the international system of units is the joule (J).

Law of Conservation of Energy

The principle of energy conservation announces that: "energy is neither created nor destroyed"; it can only be transformed. That is, we can only convert energy from one type to another.

According to the conservation law, the total energy in closed physical systems always remains constant. The concept of a closed system means that it is a system that does not exchange energy with the outside.

The transfer of energy can occur in many ways depending on the type of energy, for example:

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

When we refer to renewable or non-renewable energies, we generally refer to the energy sources with which electrical power is generated. However, these resources are often used for heat.

In this sense, we can distinguish:

  • Renewable energy is defined as that which comes from inexhaustible natural resources. Some examples of these forms of energy are solar, wind, and hydro, among others.

  • Non-renewable sources are defined as those that come from limited sources with a limited regeneration capacity. Some examples are fossil fuels (coal, oil, and natural gas) and nuclear reactors, among others.

However, the ultimate type of energy is nuclear energy. All energy sources are related in some way to solar energy. Nevertheless, the energy coming from the Sun is a consequence of multiple fusion nuclear reactions in its core. 

How Is It Used? Most Common Uses and Applications

Using energy as a source of work has always been an essential need for man. Moreover, it represents one of the fundamental factors of modern economic development and technical progress.

Until the beginning of the industrial revolution, man used several energy sources such as muscle strength, the force of the water and wind, and vegetable fuels for obtaining thermal energy.

Until then, these were the only resources used to obtain them. Over time, technology has evolved, and many other energy concepts are distinguished depending on their nature. Here we show some types of energy and their definitions:

  • Electrical power: based on the movement of ions or electrons.

  • Chemistry: the energy is stored in the molecular structure of atoms and molecules of chemical compounds.

  • Mechanic energy includes kinetic and potential energy based on the speed and position of a body.

  • Electromagnetic: generated by the presence of a magnetic field.

  • Gravitational energy: it is a kind of potential energy based on the Earth's gravity.

  • Nuclear energy: the power is stored in the nucleus of the atoms. When an atom is split, a lot of energy is released in the form of radiant energy.


Published: December 10, 2009
Last review: June 30, 2022