The purpose of this article is to reveal the essence of the concept “mechanical energy \u0026 raquo ;. Physics makes wide use of 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. Consider an example:
The figure shows a body that can be in various 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, when moving from state I to state II, the body can perform work. In carrying out the work, the mechanical state of the body changes, and the mechanical state can be characterized by one physical quantity - energy.
Energy is the scalar physical quantity of all forms of motion of matter and variants of their interaction.
What is the mechanical energy
Mechanical energy is a scalar physical quantity that determines the body’s ability to do work.
Since energy is a characteristic of the state of a system at a certain point in time, work is a characteristic of the process of changing the state of a system.
Energy and work have the same units:[A] = [E] = 1 J.
The types of mechanical energy
Mechanical free energy is divided into two types: kinetic and potential.
Kinetic energy - This is the mechanical energy of the body, which is determined by the speed of its movement.
Kinetic energy is inherent in moving bodies. Stopping, they perform mechanical work.
In different reference systems, the speeds of the same body at an arbitrary point in time can be different. Therefore, kinetic energy \u0026 ndash; relative value, it is determined by the choice of reference system.
If a force acts on the body during movement (or several forces simultaneously), the kinetic energy of the body changes: the body accelerates or stops. In this case, the work of the force or the work of the resultant of all the forces that are applied to the body will be equal to the difference in kinetic energies:
This statement and the formula given the name kinetic energy theorem .
Potential energy call the energy due to the interaction between the bodies.
When a body falls by weightm from highh gravity does the work. Since the work and the change in energy are related by the equation, we can write the formula for the potential energy of the body in the field of gravity:
Unlike kinetic energyEk potentialEp may have a negative value whenh \u0026 lt; 0 (for example, the body lying on the bottom of the well).
Another kind of mechanical potential energy is deformation energy. Compressed into the distancex spring with stiffnessk has potential energy (strain energy):
Energy deformation has found wide application in practice (toys), in the technique - automatic machines, relays and others.
Full mechanical energy bodies call 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 all interactions of bodies with each other.
Unlike impulse, which has no equivalent form, energy has many forms: mechanical, thermal, energy of molecular motion, electrical energy with the forces of interaction of charges and others. One form of energy can transfer to another, for example, the thermal kinetic energy is transferred in the process of braking the car. If there is no frictional force, and heat is not formed, then the total mechanical energy is not lost, but remains constant during the movement or interaction of the 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 type of energy can turn completely into any other kind of energy.