In Chap. 6 inductors have been analyzed. In these devices there are no moving parts. In this chapter the force ( $$ {\vec{\hbox{F}}} $$ ) and torque ( $$ {\vec{\hbox{T}}} $$ ) production in electromagnetic circuits such as magnets, actuators, relays, linear and rotating machines will be discussed. These devices have a stationary part (stator) and a moving part (rotor). Figures 9.1a, b illustrate linear asynchronous actuator fields, Fig. 9.1c a linear synchronous actuator field [1, 2], and Fig. 9.1d shows a rotary permanent-magnet actuator [3].