Sp

Space
The set of all possible points; made up of infinite planes.
Space Charge
An electrical charge distributed throughout a volume or space.
Space Diversity
Reception of radio waves by two or more antennas spaced some distance apart.
Space Frame
A series of structural members assembled to create a skeletal system that supports the interior systems as well as the exterior skin and driveline components of a vehicle.
Space Wave
Radio waves that travel directly from the transmitter to the receiver and remain in the troposphere.
Space Weather
The changing conditions in interplanetary space caused by fluctuations in the solar wind.
Spacetime
A combination of time and three-dimensional space that forms a four-dimensional geometry expressing the connections between space and time.
Spade
A sturdy digging tool with a thick handle and a heavy, flat blade that can be pushed into the ground with the foot.
Spall
Small chips or fragments which are sometimes given off by electrodes during the welding operation.
Span
The distance a bridge extends between two supports.
Spanner
A tool used to turn a nut and bolt. Wrench is another name for spanner.
Spark Advance
The number of degrees of crankshaft rotation before TDC (Top Dead Centre) where the spark plug is fired.
Spark Gap Modulator
A modulator that consists of a circuit for storing energy, a circuit for rapidly discharging the storage circuit, a pulse transformer, and a power source.
Spark Ignition Engine
An engine whereby the fuel air mixture is compressed in the cylinder and then ignited with an electric spark.
Spark Plug
Electrical device that fits into the cylinder head of an internal-combustion engine and ignites the gas by means of an electric spark.
Spark Plug Fouling
A deposit on the electrodes of a spark-plug of essentially non-conducting material that may, but will not necessarily, prevent the plug from operating.
Spark Plug Whiskering
A deposit of conductive material that tends to form a bridge between the spark-plug electrodes or to a ground, thus shorting out the plug.
Spatial Filtering
Enhancing an image by increasing or decreasing its spatial frequencies.
Spatial Power Density
The net power in a given cross sectional area of a propagating medium. Convenient units are watts (or dBm) per square meter. Spatial power density is independent of frequency.
Spatial Sampling
Sampling in two or more dimensions.
SPC
Abbreviation of Statistical Process Control.
SPDT Switch
Abbreviation of Single-Pole, Double-Throw switch.
Special Constants
A list of Mathematical constansts and their formulations.
Special Products and Factorials
e.g. (x + y)2 = x2 + 2xy + y2
Special Theory of Relativity
A comprehensive theory of space and time that replaces Newtonian mechanics when velocities get very large.
Specific Airflow Resistance
The product of the airflow resistance of a specimen and its area.
Specific Fan Power
The energy efficiency of fan air movement systems.
Specific Fuel Consumption
The amount of fuel needed to provide a given power for a given period.
Specific Gas Constant
This is the molar gas constant divided by the molecular weight of the gas in question.
Specific Gravity
The density of any material divided by that of water at a standard temperature.
Specific Heat Capacity
The amount of heat required to raise the temperature of 1kg of a substance through 1K.
Specific Humidity
Ratio of weight of vapour to the weight of gas in a unit volume of an air-water vapour mixture.
Specific Impulse
A performance parameter of a rocket engine, the thrust F in pounds divided by the weight flow rate in pounds per second.
Specific Resistance
The resistance measured in ohms of a unit volume of a substance to the flow of electric current.
Specific Volume
The volume of a unit mass of substance, the reciprocal of density.
Specimen Interaction
Reactions that occur inside the specimen when being struck with a beam of energetic electrons.
Specimen Interaction Volume
The volume inside the specimen in which all specimen interactions occur during electron beam irradiation.
Spectator Ion
An ion that appears as both a reactant and a product in an ionic equation.
Spectra
Plural of spectrum.
Spectral Balance
Balance across the entire frequency spectrum of the audio range.
Spectral Centroid
This is the centre of gravity of a frequency spectrum.
Spectral Leakage
In a Fourier Transform the signal is assumed to be periodic. If a pure sine wave does not repeat exactly within the time window, it is truncated. This truncation will lead to the frequency domain resultant being smeared (leakage) and not a single frequency.
Spectrogram
A three-dimensional intensity plot displaying the amplitude of spectral components as a function of both time and frequency.
Spectrometer
An instrument which measure the position of spectral lines.
Spectrometry
Breaking up white light into its constituent wavelengths and measuring them on a calibrated scale.
Spectrophotometer
An instrument which determines the energy distribution in a spectrum.
Spectrophotometry
Determination of the concentration of a material in a sample by measurement of the amount of light the sample absorbs.
Spectroscopy
Study of a radiation spectrum, emitted, absorbed or diffused.
Spectrum
A spectrum is a definition of the magnitude of the frequency components that constitute a quantity.
Spectrum Analyser
An instrument for measuring, and usually recording, the spectrum of a signal.
Spectrum Analysis
The display of electromagnetic energy arranged according to wavelength or frequency.
Spectrum Density
Limit, as the bandwidth approaches zero, of the mean-square amplitude divided by bandwidth.
Spectrum Signature
The power versus frequency distribution of the energy in a transmitted signal, or the response characteristic of a receiver.
Specular Reflections
Mirrorlike reflections of sound from a flat surface.
Speculum
A copper-tin alloy with 33 to 45% of tin that has very high optical reflectivity when polished.

Speech Coding
Excellent speech quality implies that coded speech is indistinguishable from the original and without perceptible noise.
Speech Intelligibility
A measure of sound clarity that indicates the ease of understanding speech.
Speech Interference Level
A calculated quantity providing a guide to the interference of a noise with the reception of speech.
Speech Privacy
There are a number of ways of classifying speech privacy.
Speech Transmission Index
A single number that indicates the effect of a transmission system on speech intelligibility.
Speed of Data Transfer
The rate at which information travels through a network, usually measured in megabits per second.
Speed of Light in Vacuo
c = 2.997924580x108 ms-1
Speed of Sound
Depends on the elastic and inertial properties of the particular medium.
SPF
A rating for lotions used to protect the skin against sunburn.
Sphalerite
The mineral name for Zinc Sulphide, the most common ore of Zinc.
Sphere
Basic calculations of the properties of a sphere.
Spherical Aberration
A defect caused by grinding the surface of a lens or mirror to a spherical rather than a parabolic shape.
Spherical Coordinates
A point is located in space by the distance from the origin and two angles.
Spherical Divergence
The condition of propagation of spherical waves that relates to the regular decrease in intensity of a spherical sound wave at progressively greater distances from the source. Under this condition the sound pressure level decreases 6 decibels with each doubling of distance from the source.
Spherical Triangles
A triangle on the surface of a unit sphere.
Spherical Trigonometry
The branch of mathematics dealing with measurements on the sphere.
Spherical Wave
Wave in which the wavefronts are concentric spheres.
Spheroid
An aggregate of iron or alloy carbides of essentially spherical shape dispersed through-out a matrix of ferrite.
Spheroidizing
Heating and cooling to produce a spherodial or globular form of carbide in steel.
Spillway
An overflow channel that allows dam operators to release lake water when it gets high enough to threaten the safety of a dam.
Spindle
The rotating part of a machine tool.
Spindle Speed
The rotational speed at which a machine is set.
Spinner
A streamlined fairing over a propeller hub.
Spinodal Structure
A fine homogeneous mixture of two phases that form by growth of composition waves in a solid solution during suitable heat treatment.
Spin-Orbit Effect
An effect that causes atomic energy levels to be split because electrons have intrinsic angular momentum in addition to their extrinsic orbital angular momentum.
Spintronics
Computer processor that uses the spin of the electron to carry information rather than the charge.
Spiral Gear
When the helical gears are not aligned so the axles are parallel they are known as spiral gears.
Spiral Wound Lead Acid Battery
Instead of having the electrodes as flat plates, the electrodes are rolled up in a spiral.
Spire
A tall, tapering, acutely pointed roof to a tower, as in the top of a steeple.
Spirit
An essence or extract that can be prepared from another substance as by distillation. Can mean alcohol.
Spirit Level
A tool for testing if a surface is level using a glass tube containing an air bubble.
Spirit of Alum
An old name for sulphuric acid.
Spirit of Hartshorn
An old name for ammonia as it was prepared from animal hooves and horns.
SPL
Abbreviation of Sound Pressure Level, ten times the logarithm of the ratio of the time-mean-square pressure of a sound to the square of the reference sound pressure.
Splash Lubrication
A system of lubrication in which parts of a mechanism dip into and splash the lubricant onto themselves and or other parts of the mechanism.
Splatter
Unwanted sideband frequencies that are generated from over modulation.
Splayed Springs
Leaf springs that are not parallel to the centreline of the vehicle in the plan view.
Splaying
Walls are splayed when they are constructed somewhat "off square", i.e., a few degrees from the normal rectilinear form.
Splice
A joint formed by the connecting of two or more parts.
Split Cycle Engine
A type of internal combustion engine that divides four cylinder strokes between two paired cylinders, one for intake/compression and another for power/exhaust.
Split Pin
A metal pin with two arms which is passed through a hole and held in place by the springing apart of the arms.
Spokeshave
Used to shape curved surfaces, consists of a blade fastened between two handles, blades come in straight, concave and convex curves.
Spontaneous Reaction
A reaction that will proceed without any outside energy.
Sporadic E Layer
Irregular, cloud-like patches of unusually high ionization.
Spring
Occurs at the intersection of the water table with the ground surface.
Spring Constant
The amount of force required to stretch a spring by 1 unit of length.
Spring Dividers
Dividers whose legs are held together at the hinged end by the pressure of a C-shaped spring.
Spring Rate
Force per unit distance of compression or extension of a spring.
Spring Top Leaf Thickness
The thickness of the topmost leaf in a multiple-leaf spring.
Springback
Degree to which a material returns to its original shape after deformation.
Springs
The physics of simple springs - helical and beam forms.
Sprocket Tuner
A mechanical tuning device for magnetron tubes that changes the frequency of the cavities by changing the inductance.
Sprues
The channels cut into a mould to allow material to flow in. Also, the name given to the parts formed by the channels when the parts are removed.
Sprung Weight
The weight supported by the suspension, including a proportion of the suspension arms.
SPST Switch
Abbreviation of Single-Pole, Single-Throw switch.
Spur Gear
A gear having teeth parallel to the axis of the shaft on which it is mounted.
Spurious Emission
Far-field electromagnetic radiation transmitted on a frequency outside the bandwidth required for satisfactory transmission of the required waveform.
Spurious Response
Any response of an electronic receiver or device to signals at frequencies other than the frequency to which it is tuned.