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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 ?
In support of this view, in a prior study of ours, we have found that crocins (15-30 mg/kg) did not affect rats' motor activity (Pitsikas et al.
Latency (40 and 80 mg/kg), time spent in lit area (40 and 80 mg/kg), motor activity (120 mg/kg), as well as total number of rearing (80 and 120 mg/kg), rearings in dark area (120 mg/kg) and rearings in lit area (all doses) were also significantly reduced after treatment with GHB, in comparison with the control group (p<0.
First, we expect to find that, of the total sample, the children who display high levels of traits that are typical of negative affect (anger, discomfort, self-soothing problems, and fear) and high levels of general motor activity will also present high levels of anxiety symptomatology.
Reliability and validity of the upper-extremity Motor Activity Log-14 for measuring real-world arm use.
In his studies of the relationship between attention and motor activity, obertson focuses on very short time scales-right down to a 60th of a second.
For example, the developmental challenges of infancy and early childhood include the establishment of a secure, reciprocal relationship with a caretaker (attachment), the emergence of self-regulatory mechanisms (eating, sleeping, etc,), development of controlled motor activity, and progress in the domains of language and cognitive skills.
For example, their hyperactivity and gross motor activity into fidgetiness and restlessness.
There are several published studies of daily motor activity patterns in leech species, but no evidence that leeches possess a circadian clock.
The largest reductions were in the premotor cortex and the superior prefrontal cortex-areas earlier shown to be involved in the control of attention and motor activity.
This volumes examines the mechanisms that underlie the generation of sensory and motor activity in the functional and dysfunctional spinal cord: a cutting-edge model system for both basic and translational neuroscience.
Regarded from this angle, motor activity for staying fit mainly aims to promote education through and for movement, and also to shape public opinion towards knowing and appreciating the benefits derived from the practice of various forms of motor activities for fitness maintenance.
We know how the neurotransmitter works, and this has enabled us to design experiments that allow us to recover motor activity, we also determined through experiments that dopamine can promote or inhibit the movement under normal conditions; the problem is knowing when it promotes and when it stops, and to perform the process it uses different receptors.