What is the meaning of the law of conservation of energy in science and technology?

The law of conservation and conversion of energy provides a scientific basis for a variety of calculations in all areas of science and technology. For example, in mechanics, knowing the internal energy of a motionless body, we can find what maximum kinetic energy it can acquire (shell), knowing the potential energy of fuel combustion, we can predict which fuel is better (engine). As a result of the discovery of the law of conservation of energy, it was proved for example that it is impossible to create a perpetual motion machine of the first (energy is released during its operation) and the second kind (it works forever, from one “push”). Knowing the energy balance of the system, scientists and engineers can predict how much of the energy can be turned into “useful” work.