The Physics of Coffee Rings Finally Explained

It’s Mon­day morn­ing. Anoth­er work week begins; anoth­er cup of cof­fee to the res­cue. If you’re not care­ful, you might spill a bit of that pre­cious cof­fee and then lat­er won­der (à la Jer­ry Sein­feld) — What is the deal with that cof­fee ring on the table? Why does it form a ring with dark, out­er edges? You can imag­ine Sein­feld ask­ing this, right?

Well, it turns out there’s an answer for this. And it comes straight from a lab­o­ra­to­ry at the Uni­ver­si­ty of Penn­syl­va­ni­a’s Depart­ment of Physics and Astron­o­my. Yes, my friends, it all comes down to the shape of the par­ti­cles in the liq­uid. Cof­fee is made up of spher­i­cal par­ti­cles, and they get dis­trib­uted uneven­ly, with some push­ing out­ward towards an edge and form­ing dark rings. Mean­while, oth­er liq­uids are made up of oblong par­ti­cles that get dis­trib­uted even­ly, hence no rings. The UPenn video above breaks it all down for you.

Amaz­ing­ly, this isn’t our first post on Physics and Cof­fee. Here’s a quick look at how they drink cof­fee at zero grav­i­ty in the Inter­na­tion­al Space Sta­tion. Enjoy!

via Radio Lab

Relat­ed Con­tent:

Every­thing You Want­ed to Know About Cof­fee in Three Min­utes

Free Online Cours­es Online about Physics from Great Uni­ver­si­ties

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