1. The problem statement, all variables and given/known data I did an experiment to separate different sizes of starch particles (range of size 1 µm to 10 µm). I mixed the starch powder with water in a long cylinder. I have to create model by using long cylinder to separate those starch particles according to their size (<1µm, <5µm.,<10 µm) with fluid outlet for each sizes. I use the Stoke's law to estimate the time of starch particle (for example for size 5 µm) left on top of the solution. but I have a problem on how to calculate/estimate the distance of 90% of 10µm starch particles in fluid (water) reach to the bottom of cylinder? and estimation of time for it to fall at the bottom. I figured out that I can use a Stoke's law but this equation could not use to estimate for how distance for 90% of 10 micrometer of starch particles reached the bottom of the cylinder. 2. Relevant equations By using the stoke's law I can estimate the time for <5 µm of starch particle left on the top. 3. The attempt at a solution Can I use the other relevant equation other than Stle's law to measure the distance of 90% 10µm starch travel until reach the bottom of cylinder? I tried to use the equation d=Vi(t)+(0.5*a*t2) but I think this equation is not relevant to my case.