I think that solid rocket motors try to achieve this, where the fuel has something of a star-shaped hole in the middle, and, as it burns, the amount of fuel exposed (surface area) stays roughly constant (so as to give a constant thrust). The hole gradually becomes "smoother", which keeps the surface area constant as the hole gets larger. Going backwards probably doesn't work, I would guess. Bill C. -----Original Message----- From: math-fun-bounces+cordwell=sandia.gov@mailman.xmission.com [mailto:math-fun-bounces+cordwell=sandia.gov@mailman.xmission.com]On Behalf Of David Wolfe Sent: Wednesday, April 26, 2006 10:27 AM To: math-fun Subject: [math-fun] A problem for the shower A question struck me in the shower this morning: Suppose you would like a piece of soap which dissolves at a uniform rate. I.e., as it gets smaller, the soap bar's surface area remains constant until it vanishes. I have convinced myself that one should be able to construct such a bar of soap with arbitrarily small holes. As the soap gets smaller, the holes are exposed to increase the surface area. Need it have holes? _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun