The purpose of this article is to reveal the essence of the concept of "mechanical energy \u0026 raquo ;. Physics widely uses this concept both practically and theoretically.

## Work and energy

Mechanical work can be determined if the force acting on the body and the movement of the body are known. There is another way to calculate mechanical work. Let's consider an example:

The figure shows a body that can be in different mechanical states (I and II). The process of transition of a body from state I to state II is characterized by mechanical work, that is, in the transition from state I to state II the body can carry out the work. When the work is done, the mechanical state of the body changes, and the mechanical state can be characterized by a single physical quantity - energy.

Energy is the scalar physical quantity of all forms of motion of matter and the variants of their interaction.

## What is the mechanical energy

Mechanical energy is defined as a scalar physical quantity that determines the body's ability to perform work.

Since energy is a characteristic of the state of the system at a certain point in time, work is a characteristic of the process of changing the state of the system.

Energy and work have the same units of measurement:*[A] = [E] = 1 J.*

## The types of mechanical energy

Mechanical free energy is divided into two types: kinetic and potential.

*Kinetic energy* Is the mechanical energy of the body, which is determined by the speed of its movement.

The kinetic energy is inherent in moving bodies. Stopping, they perform mechanical work.

In different frames of reference, the velocities of the same body at an arbitrary instant of time may be different. Therefore, the kinetic energy \u0026 ndash; relative value, it is due to the choice of the frame of reference.

If the body is acted upon by a force (or several forces at the same time), the kinetic energy of the body changes: the body accelerates or stops. In this case, the work of force or the work of the resultant of all the forces that are applied to the body will be equal to the difference of the kinetic energies:

This statement and the formula given the name *kinetic energy theorem* .

*Potential energy* called the energy due to the interaction between bodies.

When a body falls in mass*m* from high*h* the force of attraction does the work. Since the work and the change in energy are related by the equation, we can write down the formula for the potential energy of the body in the field of gravity:

In contrast to the kinetic energy*E _{k}* the potential

*E*can have a negative value when

_{p}*h \u0026 lt; 0*(for example, the body lying on the bottom of the well).

Another type of mechanical potential energy is the energy of deformation. Compressed by distance*x* spring with rigidity*k* has potential energy (deformation energy):

The energy of deformation has found wide application in practice (toys), in technology - automata, relays and others.

*Full mechanical energy* bodies are called the sum of energies: kinetic and potential.

## The law of conservation of mechanical energy

One of the most accurate tests, which were held in the mid-nineteenth century English physicist Joule and German physicist Mayer, showed that the amount of energy in a closed system remains unchanged. She just goes from one bodies to another. These studies helped to open *law of energy conservation* :

*The total mechanical energy of an isolated system of bodies remains constant for any interactions between the bodies.*

Unlike a pulse that does not have an equivalent shape, the energy has many forms: mechanical, thermal, energy of molecular motion, electric energy with charge interaction forces, and others. One form of energy can pass into another, for example, into thermal kinetic energy passes in the process of braking the car. If there is no frictional force and heat is not generated, the total mechanical energy is not lost, but remains constant in the process of motion or interaction of bodies:

When the force of friction between bodies, then there is a reduction of mechanical energy, but in this case she gets lost, and is converted to thermal (internal). If the above closed system does the work of an external force, there is an increase in the mechanical energy performed by the work force. If the closed-loop system performs work on external bodies, then there is a reduction of the mechanical energy of the system on the value of its work.

Each kind of energy can be transformed completely into an arbitrary other kind of energy.