The Figuring Physics that appeared in our April 2007 issue has drawn a number of responses. The question posed by Paul Hewitt in that piece had to do with evaporative cooling: “Consider four grams of boiling water poured onto a cold surface. Suppose one gram rapidly evaporates by absorbing 540 calories from the remaining three grams of water, ideally with no other heat transfer occurring. The remaining three grams will become (a) water at a temperature above 0°C, (b) water at 0°C, or (c) ice at 0°C.” Hewitt's answer (c) drew protests from readers who argued that this would violate the second law of thermodynamics.

Topics
Laws of thermodynamics, Thermodynamic states and processes
1.
Ronald Lane Reese, University Physics (Brooks/Cole, 2000), p. 682.
2.
David Halliday, Robert Resnick, and Jearl Walker, Fundamentals of Physics, 6th ed. (Wiley, 2001), p. 487.
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© 2007 American Association of Physics Teachers.
2007
American Association of Physics Teachers
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