1. (5 points) Which one of the following organisms can propel themselves (effectively) in
water? Justify your answer using appropriate nondimensional groups and the implications
thereof (i.e. don’t just guess based on intuition). To help with your answer, assume a
density 10
3
kg m
3
, viscosity 10
4
kg m s
2
and that an average velocity is 0.25 μm s
1
.
(a)
(b)
fins
(c)
(d)
1
µ
m
2. (10 points) Glycerin (a very viscous Newtonian fluid) is placed inside a cylindrical
container that has a concentric rotating rod (see Figure a below). At distance R from the
rotation axis, you place a blob of red dye and rotate the rod 20 times
slowly
counterclockwise until a red dye “zone” forms (see Figure b below). Answer the following
questions using appropriate nondimensional groups and the implications thereof (i.e. don’t
just guess based on intuition).
a) what will happen if you rotate the rod 20 times
slowly and clockwise
?
b) what will happen if you rotate the rod 20 times
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 Spring '08
 Staff
 Fluid Dynamics, l., 4 kg, 103 kg

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