I was watching an XKCD “What-If” video recently and Randal off-handedly mentions the title fact as a given. Upon a further Google search I see explanations about why sound moves faster in liquids than gasses but nothing for my specific question. Is there an intuitive explanation for that fact or is it just one of those weird observable facts with no clear explanation
Badically. “Liquid/fluid” and “gas” don’t necessarily mean the same thing scientifically as they do colloquially, they’re actually very close to the same thing.
Fluid dynamics covers the study of liquids, gasses, and plasmas because they’re effectively the same.
Note that the speed of sound isn’t a constant across various media. Just like the speed of light isn’t a constant on different media. The “speed of light” we usually refer to is specifically in a vacuum. Light travelling through a media like water or a prism actually changes speed, however slight.
The same happens to sound. The speed of sound at altitude is different from sea level for instance, because of the atmospheric pressure difference. And sound doesn’t propagate at all in a vacuum because it requires the wave to move molecules, which don’t exist in a vacuum.
Both, liquids and gases, are fluids. The main difference is that liquid phases have a free surface, e.g. the level of water in a glas, whereas gases don’t. Their surface is equal to the surface of their compartment.