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Re: Centrifuge

A SAMPLE OF BLOOD IS PLACED IN A CENTRIFUGE
OF RADIUS 15 CM. THE MASS OF A RED CORPUSCULE
IS 3E-16 KG AND THE MAGNITUDE OF THE FORCE
REQUIRED TO MAKE IT SETTLE OUT OF THE PLASMA
IS 4E-11 N. AT HOW MANY REVOLUTIONS PER
SECOND SHOULD THE CENTRIFUGE BE OPERATED?

I don't have the 5th edition, but the same problem appears in the 4th
edition (#34 on p. 207) with the adjective "centripetal" in front of
the word "force" in the problem statement above. Interesting that a
centripetal force can cause something to settle outward, isn't it? I
guess the editors correctly decided that wasn't such a great way to
look at things, so they dropped the adjective and left everyone to
use their ordinary understanding of centrifugal force instead
(without using such "non-PC" terms of course), as Brian and Ludwik
have pointed out.

I like to relate centrifuge problems to the idea of artificial
gravity on rotating space stations. Natural gravity is not strong
enough to cause the particles to settle out. So we put the tube into
a centrifuge in order to increase "gravity." Carl
--
Dr. Carl E. Mungan, Asst. Prof. of Physics 410-293-6680 (O) -3729 (F)
U.S. Naval Academy, Annapolis, MD 21402-5026 mailto:mungan@usna.edu
http://physics.usna.edu/physics/faculty/mungan/