ok so im making a few solenoids for a little project im doing at home, im making a mass driver. i thought it would look good on my uni application, and it would be fun to build. anyway, im using the equation http://img229.imageshack.us/img229/5841/equation1solenoidimg.png [Broken] to find the magnetic flux density of the solenoid and im using F=BIL to find the force the solenoid exerts on the ball bearing, then im using a=f/m to get the acceleration. now i dont know if im using the right equations or not because the acceleration i get is about 28000ms-2 and that seems way to powerfull for what im using. all my values are in meters, amps, Tm/A (for the permeability constant) and kilograms (wich are made into newtons by dividing by g for the mass of the ball bearing) ill just list what the values im using are. u0 = 1.26*10-6 I = 425 amps N = 60 turns of the coil r1 = 0.0175 meters r2 = 0.0195 meters X = 0.16 meters X2 = 0.22 meters L = 0.06 meters m = 1.529*10-3 (its 0.015kg divided by 9.81) i got the equation for the magnetic flux density from http://www.netdenizen.com/emagnettest/solenoids/?solenoid" and it said to use 1.26*10-6 for the permeability constant if you using meters which i am. i don't think i enter anything wrong in my calculations, i redid everything three times and still got a massive acceleration. so either i got something wrong or this thing is going to be crazy. ill attach the excel document i used for calculating the magnetic flux density, the acceleration is easy to work out from there.