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

Energy is the ability to carry out a certain job.## What is energy?

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

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

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

On the other hand, in relativistic mechanics, governed by theTheory of relativity Albert Einstein, energy and mass have a closer relationship that defines the famous equation *E = m.c2*, that is, energy equals mass timesspeed of light squared. Thus, all bodies, simply because they are composed of matter, have 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).

## Potential energy

Potential energy is associated with a body or physical system determined 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 masses very large (such as the masses of planets and the Sun). For example, a roller coaster car has a maximum potential energy at its maximum height position because it is immersed in the gravitational field of the Earth. Once the wagon is dropped, it loses height and the potential energy is transformed into kinetic energy.
**Electrostatic potential energy**. Regarding electricity also applies the concept of potential energy, which can be converted into other forms of energy, such as kinetics, thermal or light, given the enormous versatility of the electromagnetism. In this case the energy results from the field of electric 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 regain its original shape after being subjected to deformation forces greater than its resistance. A clear example of elastic energy is that of a spring that stretches or contracts as a result of 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 arc is tensioned by pulling the elastic fiber, slightly bending the wood, but still with zero speed. The next instant the potential energy becomes kinetic and the arrow is thrown at full speed forward.

## Kinetic energy

A body moving at a certain speed will have associated kinetic energy.

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

Kinetic energy is key in 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 the following:*Ec = ½.m.v2*

## Force

In physics, force It is a vector quantity (endowed with direction and sense) and is capable of modifying the amount of movement or the 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 / s2.

## Job

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

This work will be equal to the amount of energy required to move it rapidly.

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