Kelvin-Planck statement

The Kelvin-Planck statement of the second law of thermodynamics asserts that it is impossible to build a machine that operates in a cycle and produces only work while transferring heat from a single thermal reservoir. In simpler terms, no device can convert all heat energy from a hot source into useful work without some energy being lost as waste heat to a cooler environment. This principle underpins the idea that some energy will always dissipate, preventing 100% efficiency in converting heat to work, ensuring the natural flow of energy from hot to cold.