In an example, a method includes interacting electric fields from charges in conductors in different inertial reference frames to effect motion. The example method implements the mathematical framework that divides electric fields from charges in different inertial reference frames into separate electric field equations in electrically isolated conductors. The example method may implement the interaction of these electric fields to produce a force on an assembly that can, by way of illustration, propel a spacecraft using electricity without other propellant(s).