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ericmazur / PnPbook

Tracking of typos, errors, and improvements for "The Principles and Practice of Physics"
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steady flow (not the same as laminar) #69

Open JohnDenker opened 9 years ago

JohnDenker commented 9 years ago

In chapter 18 on page 473 in several places it says "laminar" flow when it surely should have said steady flow.

For example, in a low-Reynolds-number situation, a piston pump produces a non-steady flow that is laminar to a good approximation. As an even more extreme example, the velocity field associated with a planar sound wave is laminar by any reasonable definition, but not steady.

The goal of the argument appears to be non-accumulation. If you have a steady flow of a conserved quantity, then there is no accumulation anywhere. (The same line of reasoning applies verbatim to electric charge.) Laminar flow is not the right concept to be using here. Non-steady laminar flow can (and often does) result in accumulation of fluid. (Ditto electric charge.)

Also FWIW incompressibility would be sufficient ... but it is nowhere near necessary to demonstrate non-accumulation. (Ditto electric charge.)

JohnDenker commented 9 years ago

The same issue arises in the "quantitative" part of the chapter, including page 491ff.

Probably the easiest thing is to search the whole book for occurrences of "laminar". Most of them should be replaced with steady.