Fundamental
When the object rotates around the central axis, it is subjected to the centrifugal force F. When the mass of the object is M, the volume is V, the density is D, the radius of rotation is r, and the angular velocity is ω (radians/second), you can get:
F=Mω2r or F=VDω2r
The above indicates that the centrifugal force received by the centrifuged material is proportional to the mass, volume, density, centrifugal angular velocity and radius of rotation of the material. The greater the centrifugal force, the faster the centrifuged material settles.
During centrifugation, the material being centrifuged also overcomes the obstruction of buoyancy and friction. The buoyancy F} and the friction force F}} are represented by the following equations:
Where D} is the solution density, f is the friction coefficient, and is the sedimentation velocity (change in the radius of rotation per unit time). Under certain conditions, there may be
Equation (4) shows that the sedimentation velocity is proportional to the volume and density difference of the material to be centrifuged, and inversely proportional to f. If S is the settlement velocity in the unit force field (ω2r = 1), then
S is also called the sedimentation coefficient.
The sedimentation coefficient is mostly between (1~500)×10-13 seconds for biomacromolecules. For the convenience of application, it is stipulated that 1×10-13 seconds is one unit (or 1S). Generally, the simple protein is between 1 and 20S, the larger nucleic acid molecule is between 4 and 100S, and the larger subcellular structure is between 30 and 500S.
In practical applications, the centrifugal force generated by the centrifuge when working on a unit mass is expressed as a multiple of Gravity. The centrifugal force represented by this method is called relative centrifugal force (RCF), and is commonly used by “digital × gâ€. Said.
The relationship between the angular velocity ω and the rpm per minute is
ω=2πrpm / 60
So RCF=1.119×10-5·rpm2·r
According to this formula, the relative centrifugal force and the number of revolutions per minute can be interchanged, and this interchange relationship is very practical.
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