What is the RPM required if you need an RCF of 2,543 and are using a rotor with a radius of 21 centimeters?

Question

What is the RPM required if you need an RCF of 2,543 and are using a rotor with a radius of 21 centimeters?

Answer 1

When centrifuging a sample, it is often necessary to know the speed of the centrifuge required to achieve a specific relative centrifugal force (RCF). RCF is a measure of the force applied to a sample during centrifugation, and it depends on both the speed of the centrifuge and the radius of the rotor. The formula for calculating RCF is:

RCF = 1.118 x 10^-5 x r x (rpm)^2

where r is the radius of the rotor in centimeters, and rpm is the speed of the centrifuge in revolutions per minute.

To find the rpm required for a given RCF and rotor radius, we can rearrange the formula as follows:

rpm = sqrt(RCF / (1.118 x 10^-5 x r))

Substituting the given values, we get:

rpm = sqrt(2543 / (1.118 x 10^-5 x 21))

Simplifying the expression inside the square root gives:

rpm = sqrt(2543 / 0.002358)

rpm = sqrt(1079.5)

rpm = 32.89 (rounded to two decimal places)

Therefore, the RPM required for an RCF of 2,543 using a rotor with a radius of 21 centimeters is approximately 32.89 revolutions per minute.