Abstract Once a controversial idea, the fact that gases like air have weight can easily be demonstrated using reasonably precise scales in the modern teaching labora- tory. But unlike a liquid, where a mechanical model suggests a pile of hard spheres resting on each other, gas molecules are in continual motion and can have minimal interaction. How should we think about the effect these mole- cules have on the scale? And more importantly, how should we explain it to students? Several models of gas behavior are employed to answer these questions and it is shown how the weight of a gas is, like electric current, an emergent phenomena in contrast to the weight of a liquid which is direct or causal.