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Re: [Phys-l] Errata for FCI?



On Nov 3, 2010, at 7:22 AM, Chuck Britton wrote:

I'll ask again - what's WRONG with teaching the 'weight of displaced
fluid' concept. (and try to keep it simple - for us simple minded folk).

I would say that "an object experiences buoyancy" if and only if the net result of all pressure forces that act on its surface is "upward" (i.e., opposite the local free-fall acceleration in the reference frame of interest. WHEN an object experiences buoyancy, the "buoyant force" IS the net sum of those pressure forces and can be very hard to calculate. Moreover, because the net result of those forces need not be "upward" some objects simply do not "experience buoyant forces." WHEN an object is completely surrounded by a fluid that is a) in hydrostatic equilibrium and b) everywhere thick enough to be able to neglect effects like surface tension THEN Archimedes' principle applies and the buoyant force IS EQUAL TO (not "IS") the weight of the displaced fluid.

John Mallinckrodt
Cal Poly Pomona