I am confused on how a centrifuge separates particles by density. In http://en.wikipedia.org/wiki/Centrifuge" [Broken], which appears to have something to due with an applied force or centrifugal force. It would seem like the more massive particles would remain closer to the axis of rotation due to their greater mass resisting centrifugal acceleration. Does any of the seperation occur during the angular acceleration of the device up to operating angular speed, or does it all occur while spinning at constant speed? Any help will be greatly appreciated.