Conductivity Current Electric Fields Magnets Resistance Resistance, any kind of resistance, is when one force slows down or gets in the way of another force. Electrical resistance is the force that is in the way of the flow of current. There is a magic little formula used to figure out the resistance in an electrical system.
Impedance is the resistance of all the parts of a system added together.
In a metal, electrons carry the charges of the current as it flows. Nothing allows a perfect flow of current, not even super-conductors. In metal, there are tiny flaws. Not that you can see, but on a molecular level. Those imperfections cause the electrons to collide with the metal atoms.