i've been looking for an equation to find the force exerted on a ball bearing in a solenoid (on axis) using the magnetic flux density but i have no idea where to look, ive googled it, ive tried online physics enciclopedias but i just can't find it. im going through town today and im going to stop off at the libary but if you guys know anything, please post it. any help would be very much appreciated. to get the flux density im using http://img229.imageshack.us/img229/5841/equation1solenoidimg.png [Broken] EDIT: Nope they dont have anything. i read through every physics book they had in the science section and didn't find anything i didn't already know. (most of its just the same thing in 3-4 books). the guy at the help desk said its a bit to specialised. does nyone know an equation i can use? or know of a book that has it in?