Centrifugation

Centrifugation separates suspended material by its motion relative to a rotating liquid. A centrifuge rotor creates an outward centrifugal acceleration in the rotating reference frame; material denser than its surroundings tends to move outward, opposed by drag force. Collected material can form a centrifugation pellet, leaving a supernatant, or remain in separated zones within a density gradient. The useful question is which physical difference the separation exploits: a difference in sedimentation coefficient or a difference in buoyant density.
Figure 1.
Centrifuge rotor geometry and the centrifugation pellet–supernatant distinction
. Original schematic of one swung-out tube during rotation and a conceptual pelleting comparison. Rotor radius increases toward the tube's outer end. Colors and particle counts illustrate incomplete separation and trapping; they are not measured recovery fractions. The tube remains horizontal in this depiction of the rotating geometry. Details.
Centrifugation makes otherwise slow settling useful for studying biological cells, organelles, proteins and DNA. Separation and identification are different steps: a centrifugation pellet is a collected fraction, not proof that it contains only one kind of organelle. The lysozyme wall-removal experiment illustrates a complementary readout: testing material released into the separated liquid can be more informative than inspecting the retained solids.

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