Maybe I'm just dense, but... I searched for forum for "solenoid" and I still haven't found the answer that I'm looking for. Mainly, I want to know if there is a general equation for the plunger force of a solenoid-type linear actuator. I understand that the force of the plunger is related to distance in a way in the same way as a spring (but with maybe a polynomial relationship to plunger depth/distance), but I've also done some googling and I haven't found a simple general relation. I also went through several EE books and they didn't have any descriptions of how to calculate plunger force, and then went through several E&M physics books and didn't find one with equations. In fact, the one I found that described the most about solenoids with plungers was written in 1924 (Magnets by Underhill) but doesn't really have any equations. I guess I could go through and try to derive such things, but I figure it's a solved problem and my background isn't in E&M. Am I missing something here?