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16 February 2006

Coffee, Biscuits, and Physics

"To dunk is to dip biscuit, bread, cake, or doughnut into a beverage, usually hot, especially tea or coffee, but the popular American snack "milk and cookies" features cookies dunked into cold milk. Dunking a biscuit is said to release flavour, but is usually done to alter the texture of harder confections", Wikipedia. Physicist Len Fisher of the University of Bristol has presented some light-hearted discussion of dunking during the National Biscuit Dunking Day. Here is Washburn's equation, which describes capillary flow in porous materials:
Where t is the time for a liquid of viscosity η and surface tension γ to penetrate a distance L into a fully wettable, porous material whose average pore diameter is D.
Have a nice time calculating the time it takes your morning coffee to penetrate the dunked biscuits. Tags: , ,