Paddlewheel

Paddlewheel, a bearded brewer-scientist, works ropes on pulleys over a glowing copper vessel.

The Physics

James Prescott Joule let weights fall on pulleys, turning a paddle wheel inside an insulated vessel of water. Friction of the paddles warmed the water a tiny amount. Dividing the work done by the falling weights by the heat produced, he reported in 1850 (“On the Mechanical Equivalent of Heat”, Phil. Trans. R. Soc. 140, 61) that 772 foot-pounds of work raise one pound of water by 1 °F.

W = J Q

• W: mechanical work (ft·lbf)
• J: mechanical equivalent of heat (ft·lbf per BTU)
• Q: heat produced (BTU)

Heat and work are two forms of one thing, energy: the first law of thermodynamics. The SI unit of energy, the joule, is named for him.

Honest caveat: The modern value is about 778 ft·lbf/BTU (4.186 J per calorie), so Joule was within one percent.

On the sticker

Paddlewheel hauls on ropes over pulleys, above a glowing copper vessel. Printed text: PADDLEWHEEL with the line 772 ft·lbf/BTU. Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.