Hello! This site has been tremendously helpful over the past few weeks, so first off I wanted to thank the entire community here for the service your provide to others. I am doing a report on centrifuges, but before I get too far I want to make sure I understand the concept from a Newtonian perspective. I did search the topic here and elsewhere, and just want to make sure I have everything straight. Hopefully this is the right forum for this post :) That being said, here is my take on a centrifuge. Please correct any misinformation I may have gathered on the web. There are two forces which are both named "centrifugal". One is a reaction force to centripetal force, which acts upon the object causing the rotation. The other is a fictitious force which arises from observing motion from a non-inertial frame of reference, and seems to act upon the object under rotation. In actuality, from a Newtonian perspective, the object is traveling in a straight line and the centripetal force is "pulling in" the object, causing it to follow a circular path. In terms of real forces, the centripetal force acts upon the object under rotation, and the centrifugal force acts upon the object causing rotation. In terms of a simple human centrifuge (like an amusement ride, rotating upon a vertical axis with the rider strapped into the seat), the centripetal force acts upon the rider, transferred by the seat. If the rider were not strapped in ( ) they would fly off in a straight line at a tangent to their motion. The rider feels a "fictitious" centrifugal force...from their frame of reference it feels as if they are being pulled outwards. The "real" centrifugal force is a reaction force, but what does it act upon? The rotor upon the axle, or the rider upon the strap? Not sure about that one. Considering a desktop centrifuge...we have an object creating motion (say, an electrostatic motor), an axle out of the motor, a rotor attached to the axle, and tubes in the rotor. They spin up to a constant velocity, but the rotor and tubes are accelerating due to the changing direction vector. Now, the direction of the centripetal force is inward...so why would the heavier particles be at the bottom of the tube? Shouldn't the heavier particles collect on the inner wall, closest to the axis of rotation? (unless, of course, the tubes were placed horizontally; but most centrifuges I've seen have vertical tube slots in the rotors). Furthermore, is the name centrifuge a misnomer? If I am correct, it is centripetal force which causes the precipitate to collect in the tube. The centrifugal force should be acting upon the rotor by the tube, in accordance with Newton's laws. Lastly, am I missing any forces in the description of the machine? I assume I likely am when it comes to the tube and the fluid within it; I can imagine that a highly viscous fluid would be more difficult to separate, for example. I am unfamiliar to forces within fluids, so some assistance in this area would be appreciated as well. Thank you in advance for any assistance you may be able to give me, and apologies for the long post.