In his daily activities, a person uses a variety of energy: thermal, mechanical, nuclear, electromagnetic, etc. However, for now, we will consider only one of its forms - mechanical. Moreover, from the point of view of the history of the development of physics, it began with the study of mechanical motion, forces and work. At one of the stages of the formation of science, the law of conservation of energy was discovered.
When considering mechanical phenomena, the concepts of kinetic and potential energy are used. It was experimentally established that energy does not disappear without a trace, from one species it turns into another. We can assume that what has been said in its most general form formulates the law of conservation of mechanical energy.
First, it should be noted that in total the potential and kinetic energies of the body are called mechanical energy. Further, it must be borne in mind that the law of conservation of total mechanical energy is valid in the absence of external influences and additional losses caused, for example, by overcoming the resistance forces. If any of these requirements is violated, then when the energy changes, its loss will occur.
The simplest experiment, confirming the indicated boundary conditions, anyone can conduct independently. Raise the ball to a height and release it. Having hit the floor, he will jump and then fall to the floor again, and again will jump. But each time its height will be less and less until the ball freezes motionless on the floor.
What do we see in this experience? When the ball is motionless and at a height, it has only potential energy. When the fall begins, it appears speed, and therefore, kinetic energy appears. But as the fall, the height with which the movement began, becomes smaller and, accordingly, its potential energy becomes smaller, i.e. it turns into kinetic. If calculations are made, then it turns out that the energy values are equal, which means that the law of conservation of energy under these conditions is satisfied.
However, in such an example there are violations of two previously established conditions. The ball moves surrounded by air and experiences resistance on its part, albeit small. And energy is expended in overcoming resistance. In addition, the ball hits the floor and bounces, i.e. he experiences external influence, and this is the second violation of the boundary conditions that are necessary for the law of conservation of energy to be valid.
In the end, the ball will stop racing and it will stop. All available initial energy will be spent on overcoming air resistance and external influences. However, in addition to converting energy, the work to overcome the friction forces will be completed. This will lead to heating of the body itself. Often the amount of heating is not very significant, and it can be determined only when measured with precision instruments, but such a change in temperature exists.
In addition to mechanical, there are other types of energy - light, electromagnetic, chemical. However, it is true for all types of energy that a transition from one type to another is possible, and that with such transformations the total energy of all types remains constant. This is a confirmation of the universal nature of energy conservation.
Here it must be taken into account that the transfer of energy can also mean its useless loss. With mechanical phenomena, evidence of this will be the heating of the environment or interacting surfaces.
Thus, the simplest mechanical phenomenon allowed us to determine the law of conservation of energy and the boundary conditions that ensure its fulfillment. It was established that energy is being converted from the existing type to any other, and the universal nature of the mentioned law has been revealed.