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
You already got some answers, but I thought of something you might find interesting: if you had a multiple kilometers long pole in a vacuum and pushed on it, the push itself would propagate at the speed of sound!
Meaning the other end wouldn’t really move immediately, but it would instead take multiple seconds or even minutes if the pole is large enough. If it’s made of oak and is 9 km long, it would take around 3 seconds (the speed of sound in oak is around 3 km/s IIRC).
I think this was experimentally shown by a Youtuber. The speed of sound is a slight oversimplification since there are multiple types (https://www.engineeringtoolbox.com/sound-speed-solids-d_713.html)
I think Randall mentioned this at one point but I never really understood it. Is it something like on a molecular level they’re still taking some time to push in to each other? It’s so damn trippy. At what point is my long pole going to have a delay when I push it? It sounds unreal
Basically, when you push something, you push molecules, those in turn push the other molecules etc., that’s what it is.
The delay is there every time, it’s just usually really fast, the speed of sound in solid mediums is much bigger than the speed of sound in air.
There’s more delay in solid mediums than air?
Do incompressible materials therefore have extremely high speed of sound?
Yes. Nothing is truly incompressible. The speed of sound can be viewed as a measure of how much a material can squish on the atomic level before the next atoms move.
Exactly. One usually speaks of quasi-incompressibility when the resistance against compression (bulk modulus K) is much greater than the resistance against shear (shear modulus G), which is often the case for liquids such as water (strictly, fluids like water don’t have any resistance against static shear deformation, i.e. G = 0).
However, water has a lower bulk modulus (K =2 GPa) than e.g. steel (K = 160 GPa), which is considered a compressive material, as its shear modulus and bulk modulus are in the same order of magnitude (G = 81 GPa).