There are two ways that you can calculate this. 1. As Mabel stated above you need to calculate the g force that you need and then calculate the time or RPM that your centrifuge can do. or 2. (and this is the easy method) you can calculate the time based on speed or calculate the speed based on time, either way Gforce = Gforce. I choose this method because it was around before we knew about g force in centrifuges, and because I can remember it. So my first question is what are your defined constants? You state that the minimum time that your centrifuge can be set at is 1 minute. Can you adjust the speed lower than the 1800-2000 rpm? In either case your equation will look like this. (RPM1)(Time1) = (RPM2)(Time2). Solving for Time: (3500rpm)(15sec) = (1800rpm)(Xsec) =((3500)(15))/(1800) =29.16 seconds. Solving for Speed: (3500)(15) = (Xrpm)(60) =((3500)(15)/(60)) = 875 RPM If you can set your centrifuge to 875 RPM then you are good to go, and as David states you'll have to validate. Good Luck.
