Why Can You Hear the Difference Between Hot and Cold Water?

(Last Updated On: July 21, 2022)

You might have thought we missed a step by not asking if you even can hear the difference between hot and cold water. The answer, by the way, is that you can hear the difference. Even if you couldn’t put your finger on it, there’s a really good chance that you can tell the difference if you hear hot and cold water poured into a cup side by side. Plus, even if you get the answer wrong, the two definitely sound different. So why can you hear the difference between hot and cold water?

Moving Molecules

We’ve written about molecules moving around a handful of times before, but that foundation is going to be important (again) to our understanding of hearing temperature. How hot or cold something is depends on how fast the molecules that compose it are vibrating. Temperature, then, is a measure of how much those molecules are vibrating. When something is hot, its molecules are moving around a lot more than if it were cold. Intuitively, this makes sense, things are solid when they are colder and become a gas when heated enough. You can think of it like a solid object is sufficiently cold for its molecules to sit still long enough to maintain a shape.

As an aside, this doesn’t imply that the molecules are 100% still. For molecules to exhibit absolutely no movement, you’d be at absolute zero. Which is… Very cold. It’s also not really possible to achieve yet. 

Anyway, the key understanding here is that the molecules in hot water are vibrating more/faster than the molecules in cold water. 

Advertising

It looks like one of the first “hot and cold water sound” question was a British advertising firm specializing in sound design. You know, so they could make better drink ads. Makes sense, since their clients include both Coke and Pepsi. Then they contracted out a study for this and found that, yes, there was a practical reason to manipulate audio to reflect apparent temperature. 

Turns out, the vast majority of people can tell the difference between hot and cold water by sound alone.

Things settled on the viscosity of water, which does change with temperature. Viscosity can be informally understood as the thickness of a liquid. Molasses is more viscous than water. Cool. Colder water is more viscous than hot water, and that creates the difference in sound. The mechanism for this is directly related to the movement we laid out earlier. The colder (and more viscous) water has less molecular movement; the molecules are more likely to just stick together. When the water is hotter and the molecules are moving around, they’re also not really sticking together. They’re bouncing around and making smaller splashes against the inside of your glass or cup, which adds a higher-frequency layer to its sound. It also generates more steam, which changes the properties of the air sound travels in. 


See if you know your states by water body here. Try not to pour them all out in one place.

About the Author:

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Kyler is a content writer at Sporcle living in Seattle, and is currently studying at the University of Washington School of Law. He's been writing for Sporcle since 2019; sometimes the blog is an excellent platform to answer random personal questions he has about the world. Most of his free time is spent drinking black coffee like water.

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