Coffee Cup Secrets

Physicists from Yale University in New Haven, Connecticut and from the University of Bath in the U.K. took a close look downward into their mugs to find out exactly how cream blends with the coffee in a cup when stirred.

Using image tracking and infrared cameras, the researchers studied the swirl patterns formed when liquids of varying temperatures — like cold milk and hot coffee — are mixed together.

Alternating rings of the hot and cold liquids briefly form in the center of the container before moving outward toward the rim of the cup. This is the result of the slightly different viscosities of the hot and cold liquids separating out. As the temperature evens out throughout the cup, the rings break down and the liquids mix together.

By Mike Lucibella, ISNS contributor
Inside Science News Service

Read their paper on the arXiv ‘Streaks to Rings to Vortex Grids: Generic Patterns in Transient Convective Spin-Up,’ by Zhong, Patterson, and Wettlaufer.

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