Centrifugation is a standard scientific process involving rotation. Revolutions per minute, or RPM, measures how frequently a rotor arm spins; however, the radius of the rotor also factors into the force exerted at the end of the rotor arm. To standardize the forces used on different centrifuges a different measurement, called relative centrifugal force (RCF), is used; this is calculated from the RPM and the radius of the rotor, and thus is a measurement independent of the equipment used.
Things You'll Need
Determine the point in the test tube at which to calculate the RCF; measure the radius of the tube, in millimeters, at that point. Call this distance "r" and record it for later use.
Substitute the values for rpm and r into the formula for Relative Centrifugal Force:
RCF = 1.12r (rpm/1,000)^2.
For example, with an rpm of 200 and an r value of 30, the formula becomes:
RCF = (1.12 x 30) x (200/1,000)^2.
Reduce the equation to calculate the RCF value. Using the example in the previous step, the equation reduces to:
RCF = 33.6 x (0.2)^2
This further resolves to 1.1344. The resulting RCF is the rpm value converted to relative centrifugal force.
Tips & Warnings
- The RCF will vary along the length of a spinning test tube because the force is proportional to the length of the total arm; the force at the base of the test tube is greater than the force at the top of the tube.
- Always measure the arm radius in the metric system, using millimeters, rather than in standard units per standard scientific practice.
- University of Florida; McKnight Brain Institute; Cetrifugation Calculator 2; Gerry Shaw Ph.D
- Polytechnic Institute of NYU - AMPS/CBRI: Aircraft Propeller Revolutions per Minute
- University of Florida; McKnight Brain Institute; Cetrifugation Calculator; Gerry Shaw Ph.D
- Gustavus Adolphus College; Appendix F: Centrifugation; William H. Heidcamp
- Iowa State University Office of Biotechnology - Protein Facility; Introduction to Protein Techniques; 2008
- King Saud University; Physical Biochemistry 2-Hydrodynamic Methods (Sedimentation, Centrifugation and Ultracentrifugation; Gihan Gawish Ph.D.; 2011
- Photo Credit Hemera Technologies/AbleStock.com/Getty Images
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