Breathtaking Physics: Human Respiration as a Heat Engine

Breathing is something we all do, usually without thinking about it. But when viewed through the lens of physics, respiration becomes an example of elementary thermodynamics. As shown here, the lungs can be modeled as a two-stroke heat engine. Breathing thereby provides a novel physics application for life science students, demonstrating the basics of the first law of thermodynamics, coefficient of performance, and hysteresis.