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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
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


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.

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.


A machine which converts electric power into mechanical power by means of a rotating shaft.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
References in periodicals archive ?
Effects of insulin and dietary myoinositol on impaired peripheral motor nerve conduction velocity in acute streptozotocin diabetes.
We have previously demonstrated that decreased vascular reactivity by epineurial arterioles, resistance size vessels that provide circulation to the sciatic nerve, to acetylcholine precedes decrease in motor nerve conduction velocity [26].
concordance between VMT results and motor nerve conduction was good for the ulnar nerve, but very few median and common peroneal nerves with abnormal conduction had an abnormal VMT.
Median nerve Tibial nerve Peroneal nerve M-wave amplitude (mV) 4-25 7-40 -- Latency (ms) <4.5 < 7.5 < 7.0 MCV (m/s) 45-65 40-60 40-60 SNAP ([micro]V) 10-60 SCV(m/s) 45-58 Sural nerve M-wave amplitude (mV) Latency (ms) MCV (m/s) SNAP ([micro]V) 5-30 SCV(m/s) 40-60 MCV: motor nerve conduction velocity; SNAP: sensory nerve action potential; SCV: sensory nerve conduction velocity.
Our results suggest that motor nerve conduction was decreased after the nerve block technique in the ducks that exhibited wing droop and decreased wing-flapping ability.
-- polyneuropathy (paresthesias, stocking-glove sensory loss, hyperactive tendon reflexes, and slowed sensory and motor nerve conduction velocities); and
The NCS measures median and peroneal motor nerve conduction, as well as sural sensory nerve response.
Motor nerve conduction velocity (MCV), CMAP amplitude and distal motor latency (DML) were determined in the motor nerves.
Nerve conduction studies (NCSs) revealed an elongation of the distal motor latency of the left tibial nerve on the abductor hallucis muscle (4.10 ms on left side versus 3.05 ms on right side), slowing of the motor nerve conduction velocity (37.6 m/s on left side vs.
In the literature, L-I motor nerve conduction studies (NCS) performed with median-ulnar nerve stimulation were often compared with median sensory or median motor studies.
The most representative abnormalities of nerve conduction in DPN are peroneal motor nerve conduction velocity, compound muscle action potentials, distal latency, sural sensory nerve conduction velocity, sensory action potentials, and tibial distal latency [26].
Therefore, in the present study, we evaluated the findings of motor nerve conduction studies of the upper limbs in ALS patients, patients with distal-type CSA, HD patients, and SBMA patients, to investigate the pattern differences of small hand muscle involvement in these similar disorders and find some clues to differentiate between them.