Comment by numpad0

no the material inflates proportionate to absolute temperature, causing motion, iiuc

things lietrally change its volume maintaining mass when its temperature changes, due to atoms moving more energetically, like something be 4x4x4 inches at 40F, but 4 1/16 x 4 1/16 x 4 1/16" at 200F

this isn't a Stirling engine with a displacer, just a sealed off piston