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The problems you described are good and worth discussing
in the context of what we teach.
Are you saying that this is not true for the centrifuge (because objects
are microscopic)?
suppose that everything up to chapter 10 has
already been learned.
Use mud in water (instead of blood)
A uniform initial distribution of radii, from 0.0001 to 0.01 cm is probably
acceptable for a simple typical centrifuge problem.
For very small
particles (r<0.1 mm) terminal velocity is reached over
very short distance and the time to cover 25 cm is
practically equal to 0.25/vt.
r=0.1 mm --> time=6.75 seconds
r=0.01 mm --> time =675 secends
r=0.001 mm --> t=18.75 hrs
r=0.0001 mm --> t=1875 hrs = 78 days
r=0.00001 mm --> 21 years, etc.
Can somebody go one step further and show by how
much these times are reduces at 100 rev/sec ?