Finding Beauty and Truth in Mundane Occurrences. Quata Magazine
The physicist Sidney Nagel delights in solving mysteries of the universe that are hiding in plain sight. His group examined why drops of coffee (and other liquids) leave dark rings behind when they dry.
QUOTE
We’d been assuming that the overall shape of the drop stays the same as it evaporates, that it just uniformly shrinks in size — a theory that goes back to the work of Thomas Young in the early 1800s. But that’s not what it does. The drop gets pinned to the surface and then evaporates from all over, and especially from the edge. Anything that evaporates from the edge has to be replenished by a flow from the inside. That pulls the coffee to the outside, leaving a stain that’s predominantly at the edges. (Deegan et al., 1997)
Image copyright: Sidney Nagel