The basic theory of an electric motor is to convert electric power into kinetic power. Some acceptable loss of power through heat, sound and electromagnetic radiation will occur during this conversion and is an important factor in motor selection.
<explain relationship of speed, torque, voltage and current>
Motors are classified based on how they convert electrical to kinetic power. There are many types of electric motor. Some are not practical for traction applications and are therefore not mentioned in this article. Each type has distinguishing characteristics that compromise materials cost, efficiency, complexity, voltage response, torque quality, size, weight, regeneration and many other parameters.