'Electrical drives' is a general term that is commonly used to describe both DC and AC excited motors that provide continuous rotary motion, whilst 'electrical actuators' provide linear or angular displacement. Both are widely used in a variety of practical engineering systems, including machine tools, robots and aerospace systems. Other alternatives may use hydraulic or pneumatic principles to achieve similar objectives, but the electrical systems are often favoured because of the ease of control (especially using increasingly sophisticated computer based control systems) and ease of installation and transmission of energy compared to mechanical alternatives (requiring pipe-work, belts, rotating shafts etc). These, for example, are the motivations for increasing use of electrical systems in cars and 'the more-electric aircraft'.The key to the energy conversion process is the 'Lorentz force' which is the force experienced by a current carrying conductor in a magnetic field. Although there are strong parallels with electrostatic forces (i.e. the force produced on a body carrying a static charge in an electric field), almost all drives and actuators rely on electromagnetic forces.