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a. the engine, esp an internal-combustion engine, of a vehicle
b. (as modifier): a motor scooter
2. a machine that converts electrical energy into mechanical energy by means of the forces exerted on a current-carrying coil placed in a magnetic field
3. any device that converts another form of energy into mechanical energy to produce motion
a. Chiefly Brit a car or other motor vehicle
b. as modifier: motor spares
5. producing or causing motion
6. Physiol
a. of or relating to nerves or neurons that carry impulses that cause muscles to contract
b. of or relating to movement or to muscles that induce movement


A machine that converts electric energy into mechanical energy by utilizing forces produced by magnetic fields on current-carrying conductors. Also known as electric motor.
Pertaining to efferent nerves which innervate muscles and glands.
That which causes action or movement.


A machine that converts electrical into mechanical energy. Motors that develop rotational mechanical motion are most common, but linear motors are also used. A rotary motor delivers mechanical power by means of a rotating shaft extending from one or both ends of its enclosure (see illustration). The shaft is attached internally to the rotor. Shaft bearings permit the rotor to turn freely. The rotor is mounted coaxially with the stationary part, or stator, of the motor. The small space between the rotor and stator is called the air gap, even though fluids other than air may fill this gap in certain applications.

In a motor, practically all of the electromechanical energy conversion takes place in the air gap. Commercial motors employ magnetic fields as the energy link between the electrical input and the mechanical output. The air-gap magnetic field is set up by current-carrying windings located in the rotor or the stator, or by a combination of windings and permanent magnets. The magnetic field exerts forces between the rotor and stator to produce the mechanical shaft torque; at the same time, in accord with Faraday's law, the magnetic field induces voltages in the windings. The voltage induced in the winding connected to the electrical energy source is often called a countervoltage because it is in opposition to the source voltage. By its magnitude and, in the case of alternating-current (ac) motors, its phase angle, the countervoltage controls the flow of current into the motor's electrical terminals and hence the electrical power input. The physical phenomena underlying motor operation are such that the power input is adjusted automatically to meet the requirements of the mechanical load on the shaft. See Electromagnetic induction, Magnet, Windings in electric machinery

Both the rotor and stator have a cylindrical core of ferromagnetic material, usually steel. The parts of the core that are subjected to alternating magnetic flux are built up of thin steel laminations that are electrically insulated from each other to impede the flow of eddy currents, which would otherwise greatly reduce motor efficiency. The windings consist of coils of insulated copper or aluminum wire or, in some cases, heavy, rigid insulated conductors. The coils may be placed around pole pieces, called salient poles, projecting into the air gap from one of the cores, or they may be embedded in radial slots cut into the core surface facing the air gap. In a slotted core, the core material remaining between the slots is in the form of teeth, which should not be confused with magnetic poles. See Eddy current

Direct-current (dc) motors usually have salient poles on the stator and slotted rotors. Polyphase ac synchronous motors usually have salient poles on the rotor and slotted stators. Rotors and stators are both slotted in induction motors. Permanent magnets may be inserted into salient pole pieces, or they may be cemented to the core surface to form the salient poles.

The windings and permanent magnets produce magnetic poles on the rotor and stator surfaces facing each other across the air gap. If a motor is to develop torque, the number of rotor poles must equal the number of stator poles, and this number must be even because the poles on either member must alternate in polarity (north, south, north, south) circularly around the air gap.


A machine which converts electric power into mechanical power by means of a rotating shaft.
References in periodicals archive ?
However, for these severe motor dysfunction patients, biomechanical signals were very weak or abnormal, and it was also very difficult to collect.
Candesartan significantly improved the TAA-induced motor dysfunction in a dose-dependent manner, in which the higher dose group showed non-significant difference from the normal control group.
However, another child with spastic quadriplegia who is on level I (mild GMD) faces less risk of these impairments by being independently mobile and having less severe motor dysfunction.
All 9 infants had oral motor dysfunction for pureed food, as demonstrated in the SOMA assessment.
In animal studies, exercise has also been reported to reduce glutamatergic synaptic activity, decrease striatal glutamate levels, and improve motor dysfunction [8-10].
Since the motor dysfunction in MSA-C is due to the combined effect of pre- and postsynaptic receptors of the dopaminergic nerve, it is difficult to correctly assess the degeneration of dopaminergic neurons with only the F-18 FP-CIT PET showing only presynaptic DAT.
Brainstem or motor dysfunction resolved in 77% of cases by 2 months and in 90% of cases at 12 months.
The 14 patients (11 male, 3 female) with scores less than the median of 35 were assigned to the low motor dysfunction (LMD) group; the other 15 patients (8 male, 7 female) with scores equal to or greater than 35 were assigned to the high motor dysfunction (HMD) group.
Some of the common symptoms of glioblastoma multiforme are increased intracranial pressure resulting in nausea, vomiting, and headache, cognitive and visual impairment, motor dysfunction, seizures, loss in sensory functions, and changes in personality, mood or concentration.
These findings indicate that mGlu4 PAMs are not only protective against motor dysfunction in PD, but also have anti-inflammatory properties suggesting their potential as novel therapeutic agents for the treatment of PD.
In both groups, 27% of children showed definite motor dysfunction. On all other assessments, the children in both groups had similar results and no differences reached statistical significance.