Acceleration of a Medical Centrifuge

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Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
Giancoli, Douglas C. Physics. New York: Prentice Hall, 1980: 27-31. "An ultra centrifuge rotor rotates at 50,000 rpm. The top of a tube is 6.0 cm and the bottom is 10 cm, from the axis of the rotation. Calculate the centripetal acceleration in "g"s. Solution 2.7 × 106 m/s2 or 2.6 × 105 g" 260,000 g
"Centrifuging." Van Nordstrom's Scientific Encyclopedia. 1991. "The equipment used [centrifuge...] at high speed to impart a force up to 17,000 times the force of gravity higher in a centrifuge." 17,000 g
Frazier, Howard S., Arthur Sicular, and A.K. Solomon. Potassium Uptake by the Dog Erythrocyte [pdf]. Journal of General Physiology. (23 November 1953): 631–641. "Separation of red and white cells was accomplished by immediate centrifugation of the hemparinized blood at 10,000 g for 30 minutes." 10,000 g
"Centrifuge." World of Biology. The Gale Group. "In 1923 a Swedish chemist, Theodor Svedburg, developed a faster centrifuge that could a force 100,000 times greater than normal gravity. By 1936, Svedburg had perfected the ultracentrifuge that spun at 120,000 times per minute and created a centrifugal force equal to 525,000 times that of normal gravity." 100,000–525,000 g
Nelson, John B. Acute Hepatitis Associated with Mouse Leukemia II [pdf]. Journal of Experimental Medicine. (19 May 1952): 303–312. "Low speed supernatants from other liver suspensions were centrifuged in a small angle centrifuge at a speed of 5,000 rpm for 45 minutes (3500 g)" 3500 g

A force that causes motion in a curved path is directed toward the center of the path. This force is the centripetal or the center seeking force. The centripetal force is equal to the mass of the object times its velocity squared over the radius of its path. When an object rotates a centripetal force that is directed toward the center of the object itself acts upon it.

A centrifuge is a machine that puts an object in rotation around a fixed axis. All Centrifuges act on a common principle, A sample which is made up of particles of different densities is accelerated into motion around a common center. The greater the acceleration, the easier it is to separate the particles. The medical centrifuge is an essential technological advancement for biologists, chemists, lab technicians and even doctors. Medical centrifuges allow the separation of viruses, small cell parts, proteins and nucleic acid molecules. Such substances are held together by gravity; therefore, in order to separate them quickly a centrifuge must give them acceleration greater than gravity.

The speed of medical centrifuge and any rotating object is a vector quantity called the angular velocity. Angular velocity (ω) is equal to the velocity (v) of the object times the sine of the angle between its velocity and radius (θ) divided by the radius (r).

ω = v sin θ / r

With the knowledge of angular velocity and radius it is possible to find its acceleration. In this case, acceleration (a) is equal to the square of the angular velocity (omega) times the radius (r). The acceleration of a medical centrifuge typically ranges from 1000 to 100,000 times the acceleration of gravity on the surface of the earth.

Elina Slobod -- 2008


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