4.7. The law of conservation and transformation of energy

Consider the process of changing the state of the body raised to a height h. Moreover, its potential energy

The body began to fall freely . It is known from kinematics that when it reaches the surface of the earth it will have a speed ikinetic energy:

The kinetic energy of a body that fell from a height h turned out to be equal to its potential energy, which it had before the fall. Consequently:

On the surface of the earth h = 0 and potential energy , but is maximum. At the beginning of the fall , but those. potential energy is converted (converted) into kinetic. Thus, when a body falls in a body-to-earth system, the kinetic energy increases and, consequently, its change equal to work , has a positive sign, i.e.

(4.12)

The potential energy decreases, and, consequently, its change has a minus sign. Therefore, we can write:

(4.13)

Adding (4.12) and (4.13), we get

or

Amount represents the total energy and therefore

, but

(4.14)

Thus, the energy of a closed conservative system remains constant for all processes and transformations occurring in it. Energy can transfer from one species to another (mechanical, thermal, etc.), but its total amount remains constant. This provision is called the law of conservation and transformation of energy.