An electric motor is a machine that converts electrical energy into mechanical energy, usually rotational motion, by exploiting interactions between magnetic fields and electric currents. Unlike an internal-combustion engine, which converts chemical energy from fuel into mechanical work through combustion and expanding gases, an electric motor produces torque through electromagnetic forces.
The basic physical principle is that a current-carrying conductor experiences a force when it is placed in a magnetic field, while electromagnetic fields generated by coils can interact with permanent magnets or other magnetic fields. Motors are therefore fundamental components of electric vehicles, industrial machinery, pumps, fans, compressors, robots, household appliances, power tools and countless other systems. A motor normally consists of stationary components called the stator and a moving component called the rotor, together with bearings, electrical conductors, insulation, a shaft and structural components.
The stator and rotor form the central electromagnetic system of a conventional rotating motor. The stator is the stationary part that produces or shapes a magnetic field, while the rotor rotates in response to electromagnetic torque. In an alternating-current motor, the stator windings can be supplied with currents whose phase relationships create a rotating magnetic field. The rotor responds to this rotating field, producing continuous rotation.
In a permanent-magnet motor, permanent magnets provide part of the magnetic field, whereas an induction motor generates rotor magnetism through electromagnetic induction rather than permanent magnets. Motor torque is related to the strength and orientation of interacting magnetic fields and currents, while rotational speed is affected by electrical frequency, voltage, load and motor design.
Electric motors exist in numerous designs because different applications require different combinations of torque, speed, efficiency, cost, controllability and durability. Common types include brushed DC motors, brushless DC motors, induction motors, permanent-magnet synchronous motors, synchronous reluctance motors and switched-reluctance motors. Brushed motors use mechanical commutators and brushes to switch current and are comparatively simple, but brushes wear and create friction and electrical arcing. Brushless and many AC motors replace mechanical commutation with electronic control. Induction motors are robust and avoid permanent magnets, while permanent-magnet synchronous motors can provide high efficiency and power density. The choice of motor therefore depends on the complete system rather than on one universally superior design.
An electric motor's electrical characteristics are commonly described using voltage, current, power, torque, speed and efficiency. Electrical input power is approximately the product of voltage and current for a DC system, while AC systems require consideration of phase relationships and power factor. Mechanical output power for a rotating motor is related to torque and angular velocity, expressed as the product of torque and rotational speed in compatible units.
Efficiency is the ratio of mechanical output power to electrical input power, with losses occurring through winding resistance, magnetic hysteresis, eddy currents, bearing friction, aerodynamic drag, switching electronics and other mechanisms. Motor efficiency is not constant across all operating conditions; it generally varies with speed and load, which is why motor-control systems often seek operating regions that minimise energy losses.
Electric motors require control systems when precise speed, torque or direction is needed. Modern variable-speed drives and motor inverters use power electronics to regulate voltage, current and frequency supplied to the motor. In an electric vehicle, the traction inverter converts the battery's direct-current electricity into controlled currents suitable for the traction motor and continuously adjusts the electromagnetic field to control acceleration and speed. Sensors or sensorless estimation techniques can provide information about rotor position and operating conditions. Electronic control allows an electric motor to deliver high torque from low speed, operate efficiently across a broad range and reverse direction without a conventional multi-speed gearbox. This controllability is one reason electric motors are particularly useful for vehicle propulsion.
Electric motors can also operate as generators. If an external mechanical force drives a motor's rotor, electromagnetic induction can produce electrical energy instead of consuming electrical energy to create mechanical motion. This reversible behaviour is central to regenerative braking in electric and hybrid vehicles. During braking, the vehicle's wheels can drive the electric machine, causing it to operate as a generator and convert part of the vehicle's kinetic energy into electrical energy. The resulting electricity can be directed through power electronics into the traction battery, subject to battery acceptance limits and system controls. The distinction between motor and generator is therefore primarily about the direction of energy conversion rather than an entirely different physical principle.
Electric motors have several important practical advantages over combustion engines. They can achieve high efficiency, provide rapid torque response, operate quietly, contain relatively few moving parts and avoid combustion-related exhaust emissions at the point of use. They can also be integrated into compact systems and controlled very precisely. Their limitations depend on application and design and can include thermal management requirements, inverter losses, material requirements, manufacturing complexity and, for some permanent-magnet designs, dependence on particular magnetic materials. Motor performance is also constrained by temperature because excessive current and heat can damage windings, insulation, magnets or bearings. Cooling systems are therefore important in high-power applications such as electric vehicles and industrial drives.
The electric motor is consequently a general-purpose electromagnetic energy-conversion device rather than a single specific machine design. Its operation links electrical engineering, electromagnetism, materials science, mechanical engineering and power electronics. In transport, motors provide propulsion and can recover energy during deceleration; in industry, they provide controlled mechanical power for machinery; and in everyday devices, they drive fans, pumps, compressors and actuators. Understanding an electric motor requires distinguishing its electromagnetic operating principle from its particular construction, distinguishing the motor from its inverter or controller, and recognising that performance depends on the combined characteristics of the motor, power source, control system, mechanical load and thermal environment.
