We explain what energy is in physics, what potential and kinetic energy consist of. Also, how force acts and what work is.

## What is energy?

In physics, we refer to energy as **the ability of a system or phenomenon to carry out a given job**. The word energy comes from the Greek *energetic* which means “action force” or “work force.” It is a concept widely used in this science and in others in general, with various meanings and meanings.

This ability to carry out work is key to physics' interest in energy, since this discipline studies the systems of nature as actions and reactions in which matter is interrelated and energy is transferred from one system to another, one form to another.

In fact, **the energy** **It is governed according to the Second Law of Thermodynamics** (in classical Mechanics, that is, Newtonian), which establishes that the amount of energy in the universe is always stable, permanent and can neither be created nor destroyed, only transformed.

On the other hand, in relativistic mechanics, governed by Albert Einstein's Theory of Relativity, energy and mass have a closer relationship that defines the famous equation * E = mc^{2} *that is, energy is equal to mass times the speed of light squared. Thus, all bodies, simply because they are composed of matter, possess an amount of energy given by Einstein's equation.

On the other hand, **energy (E) and work (W) are equivalent** so they are measured in the same type of units: Joules or Joules (J), that is, Newtons per meter (N/m).

See also: Power in physics

## Potential energy

Potential energy is associated with a certain body or physical system by virtue of its position or height, that is, based on a field of forces in which it is immersed. This type of energy can be classified into:

**gravitational potential energy**. It is the energy that a massive body possesses when immersed in a gravitational field. Gravitational fields are created around objects with very large masses (such as the masses of planets and the sun). For example, a roller coaster car has maximum potential energy at its highest position because it is immersed in the Earth's gravitational field. Once the car drops, it loses height and the potential energy is transformed into kinetic energy.**electrostatic potential energy**. In terms of electricity, the concept of potential energy also applies, which can be converted into other forms of energy, such as kinetic, thermal or light, given the enormous versatility of electromagnetism. In this case the energy results from the field of electrical forces produced by the charged particles.**elastic potential energy**. Elastic potential energy has to do with the property of elasticity of matter, which is the tendency to recover its original shape after having been subjected to deforming forces greater than its resistance. A clear example of elastic energy is that of a spring that stretches or contracts due to an external force and returns to its original position once that force is no longer applied. Another example is the bow and arrow system. In the latter, the elastic potential energy reaches its maximum value as the bow is tensioned by pulling the elastic fiber, slightly bending the wood, but still with zero speed. At the next instant the potential energy becomes kinetic and the arrow is thrown at full speed towards the front.

## Kinetic energy

Kinetic energy is the energy of motion, and is usually designated by the signs *K*, *T* either *Ec*since it is extremely important for the various fields of physics. **A body moving at a given speed will have associated kinetic energy**.

Kinetic energy is key to the concept of temperature, in fact **the temperature** **is the kinetic energy of the ** **particles** that make up one of a substance or object.

The traditional formula for calculating the kinetic energy of a body moving at a speed (v) is as follows: **Ec = ½.mv ^{2}**

See more: Kinetic energy

## Force

In physics, force is a vector magnitude (endowed with direction and meaning) that is capable of **modify the momentum or shape of a given body or material**. It is not equivalent to effort or energy.

Force is measured in the International System by Newtons (N). One Newton is defined as the amount of force necessary to accelerate an object of mass 1 kg by 1 m/s.^{2}.

## Job

In Newtonian (classical) physics, the work of a force is defined as **the product of the force and the distance across which that force is applied. **

This work will be equivalent to the amount of energy required to move it accelerated.

Work is represented by the symbol *W* (from English *work*), is a scalar magnitude (without direction) and is expressed in the same units as energy (joules).