The amount of time needed to reproduce centrifugation conditions using a different rotor can be estimated once the relative centrifugal forces are known.
time in minutes needed for alternate rotor =
= (time in minutes for original rotor) * (relative centrifugal force for original rotor) / (relative centrifugal force for alternate rotor)
If the equation for relative centrifugal force is entered into this equation, then:
time in minutes needed for alternate rotor =
= (time in minutes for the original rotor) * (((RPM for old rotor)^2) / ((RPM for new rotor)^2)) * ((radius of old rotor in cm) / (radius of new rotor in cm))
Sources of variation in centrifugation time, in addition to relative centrifugal force include:
(1) time for rotor to reach operating speed
(2) deceleration time
(3) kind of rotor
(4) effective path length for sedimenting particles
The time estimate using a different rotor is most accurate when these variables are the same, with the only variation between the rotors being the relative centrifugal force.
