Turn a cup of hot water into a working heat engine

The Hot Water Stirling Engine is a tabletop thermodynamic model that runs on nothing more than the temperature difference between a cup of hot water and the cooler air above it. Place the engine on a mug of hot water, give the flywheel a gentle push, and students watch a real heat engine convert thermal energy into continuous mechanical motion — no fuel, no batteries, no flames.

Why Teachers Love It

• Runs on Classroom-Safe Hot Water – No open flames, no alcohol burner, no pressurized steam. Hot tap water or coffee is all it takes, making this safe and practical for demos at any grade level.
• Visible Piston Motion Teaches the Cycle – The transparent chamber lets students observe the displacer piston as it moves through compression and expansion, connecting the physical mechanism to the thermodynamic P–V diagram.
• Temperature Difference Is the Variable – As the water cools, the engine slows, giving students a live demonstration that engine output depends directly on the temperature gradient, which is a core concept of thermodynamics and the Carnot limit.