I was reading http://www.rossdecco.com/pdf/how_a_dc_solenoid_works.pdf about push and pull solenoids. I don't quite understand what differentiates the two in terms of construction. What I have is a copper wire wound around a tube and the ends are attached to a battery, like in this I believe in this video it is a pull solenoid. How is the push constructed differently from the pull exactly? What can I do to construct that same thing seen in the video into a push type? Is it just a matter of length of the plunger?