Problem #21 from College Physics of Serway& Faughn
(5th edition, page 211) asks students to calculate v when
m, R and F=(m*v^2)/R are given. The answer one gets
(150 rev/s) is the same as that shown in the book. Note
that R is "the radius of the centrifuge".
The problem defines F as "the force required to make
it [particle of mass m] settle out of the plasma". Most
blood particles are initially at r<R.
.
Since v=w*r one has F=m*r*w^2. At a constant w
F increases when r increases. Does this mean that
particles at r<R will not settle at 150 rev/sec?
What is a better way to formulate the centrifuge
problem in a non-calculus physics course?
Ludwik Kowalski