This theorem implies that bacterial flagella must act like corkscrews or flexible oars, not like stiff oars. For 10 points each:
[10h] Name this theorem, posed in Edward Purcell's paper Life at Low Reynolds Number, which states that, when viscous forces are dominant, a swimming organism cannot achieve net propulsion with a time-reversible swimming motion.
ANSWER: scallop theorem
[10m] This term describes fluid flow whose Reynolds number is much smaller than 1. A sphere moving through this kind of flow experiences a viscous force equal to 6 pi times radius times viscosity times velocity.
ANSWER: Stokes flow [or creeping flow] (The second sentence refers to Stokes's law.)
[10e] Purcell derives the scallop theorem by noting that, at low Reynolds number, the only non-zero terms in the Navier-Stokes equations are the Laplacian of fluid velocity, and the term for this quantity, whose SI unit equals one Newton per meter squared.
ANSWER: pressure
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