I'm part of a design group for a university design course and we need to launch a mass using the solenoid idea (iron rod wrapped with wire). The problem that I am having is calculating the force produced by the electromagnet given a certain voltage and current. I know that F=q(v x B) in this equation we are assuming that the field is perpendicular so what we have is just F=qvB What I need is an expression that gives the force produced by the electromagnet as a function of variables that I can find, such as voltage, current.... In the above equation, I'm trying to find the force but I do not know what v is and q. q is the charge but how do I measure that? Any help would be beneficial.