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DiracDelta - Science & Engineering encyclopedia Category: Sciences > Science & Engineering Date & country: 01/12/2007, UK Words: 4470

Springs
function init(){}Active Coils Those coils which are free to deflect under load.Angular relationship of endsThe relative position of the plane of the hooks or loops of extension spring to each other.Beam fixed at each end, load in centrewhereE = Youngs modulus [Nm^-2]I = area moment of inertia [m⁴]l = length [m]

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. See also: Casting.

Spur Gear
A gear having teeth parallel to the axis of the shaft on which it is mounted. See also: Gear Design, Gear Noise.

Square
A number raised to the power 2 ie 2 x 2 = 2² = 4. Also, a 2 dimensional figure with the height and width having the same lengths,and at right angles to each other.function init(){}

Square Root
The square root of a number is a number that when multiplied by itself equals the number that the square root is being taken of.function init(){}

Square Root of 2
The diagonal of a square of unit side. = 1.4142135623730950488 .......He is unworthy of the name of man who is ignorant of the factthat the diagonal of a square is incommensurable with its side.Plato (427-347 BC)

Square root of -1
The square root of -1 is i. See also: Imaginary Number, Square Root.

Square Wave
A periodic wave that alternately assumes one of two fixed values (high and low)with the transition time between these two levels being negligible.Square Wave, Sine SeriesSquare Wave, Cosine Series

Squeak
A sound resembling that of an unlubricated hinge. See also: Acoustics, Rattle, Sound.

Stagnation Enthalpy
The total energy or heat content of a system generated when the flow is brought to rest (zero velocity) isentropically at a stagnation point. See also: Enthalpy.

Stainless Steel
Any steel containing at least 10.5% Cr as the principal alloying element, although lesser amounts of chromium are found in stainless products such as those used for automobile mufflers. Stainless steels have the properties of being highly resistant to corrosion attack by organic acids, weak mineral acids, atmospheric corrosion, etc. Some standard g…

Standard Atmosphere
Conversions1 bar=1x10⁵ Pa1 standard atmosphere (atm)=1.01325x10⁵ Pa1 lbf in^-2 (psi)=6894.76 Pa1 tonf in^-2=15.4443x10⁶ Pa1 torr=1 mmHg1 mmHg=133.322 Pa1 inHg=3386.39 Pattle='Pressure';xiunt='Pa';yiunt='atm';mconv=101325.0;cconv=0.0; See also: Air, Atmospheric Pressure, Pressure.

Standard Deviation
Standard deviation is the square root of the variance, i.e. the square root of themean of the squares of the deviations from the mean value of a vibrating quantity.The square of the standard deviation is the variance. An expression of the so-called'second moment,' which describes the 'dispersion' or variability around the mean.In noise data, the st…

Standard Error
The standard error of the mean. The standard deviation divided by the square root of the number of data values. The extent to which we expect the sample mean to differ (+/-) from the population mean. The more data we have, the smaller this range becomes; but to get 10x the precision, we need 100x as much data. See also: Mean, Standard Deviation, St…

Standard Integrals
A listing of the standard indefinite and definite integrals.Indefinite Integralsforforfor

Standard Model
Physicists' name for the theory of fundamental particles and their interactions. It is widely tested and is accepted as correct by particle physicists. See also: Electroweak Interaction, Fundamental Interaction.

Standard Normal Distribution
A normal distribution with a mean equal to 0 and a standard deviation equal to 1 See also: Statistic, Student's t Distribution.

Standard Temperature and Pressure
Often abbreviated as stp or STP it is a temperature of 0°C and a pressure of 101325Nm^-2. See also: Pressure.

Standard Wire Gauge
A numbering system for standard wire diameters, often abbreviated as SWG.SWG gauge no.Diameter InchesDiameter mm7/00.50012.76/00.46411.7865/00.43210.9734/00.40010.1603/00.3729.4492/00.3488.83900.3248.23010.3007.62020.2767.01030.2526.40140.2325.89350.2125.38560.1924.87770.1764.47080.1604.06490.1443.658100.1283.251110.1162.946120.1042.642130.0922.337…

Standing Wave
The interference pattern produced by two waves of equal amplitude and frequency travelling in opposite directions. The pattern is characterized by alternating nodal and antinodal regions. Only the standing wave, the interaction of these two waves meeting, is stationary.AcousticsIn room acoustics, an apparently stationary waveform created by multipl…

Star
A ball of mostly hydrogen and helium gas that shines extremely brightly. Our Sun is a star. A star is so massive that its core is extremely dense and hot. At the high stellar core temperatures, atoms move so fast that they sometimes stick to other atoms when they collide with them, forming more massive atoms and releasing a great amount of energy. …

Starburst Galaxy
Galaxy in which a large burst of star formation is observed. The characteristic signature of this type of galaxy is the intense emission in the far-infrared waveband.

Stat-
Prefix to a unit in the obsolete electrostatic system of units. These units are also indicated by the notation esu (as in 'ampere esu'). See also: Statampere, Statcoulomb, Statfarad, Stathenry, Statmho, Statohm, Statvolt, Statwatt.

Statabampere
The unit of current in the obsolete electrostatic system of units.ttle='statampere';xiunt='ampere';yiunt='statampere';mconv=3.336e-10;cconv=0.0; See also: Ampere, Stat-.

Statcoulomb
The unit of charge in the obsolete electrostatic system of units.ttle='statcoulomb';xiunt='C';yiunt='statcoulomb';mconv=3.335641e-10;cconv=0.0; See also: Coulomb, Stat-.

State
Solution to Schroedinger equation defined by a unique set of quantum numbers.

State Property
A state property is a quantity that is independent of how the substance was prepared. Examples of state properties are altitude, pressure, volume, temperature and internal energy.The state of a simple compressible system is completely specified by two independent, intensive properties. Two properties are independent if one property can be varied wh…

Statfarad
The unit of capacitance in the obsolete electrostatic system of units.ttle='statfarad';xiunt='farad';yiunt='statfarad';mconv=1.113e-12;cconv=0.0; See also: Farad, Stat-.

Stathenry
The unit of inductance in the obsolete electrostatic system of units.ttle='stathenry';xiunt='henry';yiunt='stathenry';mconv=8.987552e11;cconv=0.0; See also: henry, Stat-.

Static Equilibrium
Equilibrium which does not include inertial forces. See also: Dynamic Equilibrium, Equilibrium.

Static Friction
The frictional force between two surfaces at rest relative to each other. Sometimes referred to as stiction. ExamplesMaterialStatic frictionSliding frictionBrakes~0.30.3 - 0.7Clutches0.3 - 0.40.3 - 0.7Earth - Earth0.25 - 1.0 Lignum vitae - Steel 0.1Metal - Metal (dry)0.15 - 0.60.1 - 0.5Nylon - Steel 0.3 - 0.5Perspex - Steel~0.5 PTFE - Steel 0.05 - …

Static Limit
The distance from a rotating black hole where no observer can possibly remain at rest (with respect to the distant stars) because of inertial frame dragging; this region is outside of the event horizon, except at the poles where it meets the horizon at a point. The region between the event horizon and the static limit is called the ergosphere. See …

Static Random Access Memory
An integrated circuit similar to a DRAM (dynamic random access memory) with the exception that the memory does not need to be refreshed. Unlike volatile memory (ie, DRAM), SRAM retains its contents even when the main current is turned off. See also: Memory, Synchronous Dynamic Random Access Memory.

Statically Determinate
A statically determinate structure is one where there is only one distribution of internal forces and reactions which satisfies equilibrium. In a statically determinate structure, internal forces and reactions can be determined by considering nothing more than equations of equilibrium. See also: Statically Indeterminate.

Statically Indeterminate
A statically indeterminate structure is one where there is more than one distribution of internal forces and/or reactions which satisfies equilibrium. See also: Statically Determinate.

Statistic
Anything that can be calculated from a sample of data. The most common use of the word is for summary measures such as the sample mean and sample standard deviation, although graphical displays such as histograms are also statistics. When referring to the population mean or standard deviation, the term parameter is used.Descriptive StatisticsInvolv…

Statistical Energy Analysis
A technique for analyzing the propagation through, and the sound radiation from, complex structures.

Statistical Model
A statistical model is used to describe the relationship between a dependent variable Y and one or more independent variables. See also: Statistic.

Statmho
The unit of conductane in the obsolete electrostatic system of units.ttle='statmho';xiunt='siemens';yiunt='statmho';mconv=1.11265e-12;cconv=0.0; See also: Conductance, Mho, Stat-.

Statohm
The unit of resistance in the obsolete electrostatic system of units.ttle='statohm';xiunt='ohm';yiunt='statohm';mconv=898.7552e9;cconv=0.0; See also: Ohm, Stat-.

Statvolt
The unit of electromotive force in the obsolete electrostatic system of units.ttle='statvolt';xiunt='statvolt';yiunt='volt';mconv=1/299.7925;cconv=0.0; See also: Stat-, Volt.

Statwatt
The unit of current in the obsolete electrostatic system of units.ttle='statwatt';xiunt='watt';yiunt='statwatt';mconv=1e-7;cconv=0.0; See also: Stat-, Watt.

Steam Engine
An engine that uses steam to produce useful work.The first steam locomotive was built in 1803 by Richard Trevithick. Sadly he was ahead of his time and the locomotives he built were unreliable or too heavy for the cast iron rails on which they ran.The steam locomotive was the mainstay of the railway systems across the world until the 1960's.The tra…

Steam Point
The temperature at which pure water can exist in equilibrium with water vapour at standard atmospheric pressure. See also: Ice Point, Kelvin, Triple Point.

Steam Turbine
A turbine driven by steam expansion through the blades of the turbine.Historical Notes1884 Charles Parsons patents the steam turbine.

Steel
An iron-based alloy containing manganese, usually carbon, and other alloying elements. Steel contains anywhere between 0.2% carbon for soft wire and sheet steel and 1.5% carbon for cutting tools.

Steering Offset
The distance from the point where the steering axis intersects the ground to the longitudinal line that runs through the centre of the tyre's contact patch.Sometimes called scrub radius.Zero-Offset SteeringA steering system whose geometry has a scrub radius of zero. This configuration minimizes the steering effects produced during acceleration (wit…

Stefan-Boltzmann Constant
s = 5.67x10^-8 Wm^-2K^-4ttle='Stefan-Boltzmann Constant';consttxt='s';constval=5.67e-8;constunt='Wm^-2K^-4'; See also: Physical Constants.

Stellar
Of the stars. See also: Star.

Stellar Wind
A steady or unsteady outflow of material from the surface of a star. See also: Star.

Step Response
The response of a system to an instantaneous jump in the input signal.

Step Stressing
stresses in a series of pre-selected increments. See also: Stress.

Stepper Motors
Stepper motors are a special case of Brushless DC Motors. Construction is identical except that they contain no position sensors. Excitation is sequentially applied to the windings, creating the rotating field to produce torque.Uses:Low torque applicationsOpen loop micropositioningTimer switchingAdvantagesSimplicityCompatability with digital contro…

Steradian
An SI supplementary unit.The steradian is the solid angle, having its vertex in the centre of a sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of equal length to the radius of the sphere.The surface of a sphere subtends an angle of 4 steradians at its centre.

Stereo
From the Greek meaning solid. The purpose of stereo is not to give you separate right and left channels, but to provide the illusion of a three-dimensional, holographic image between the speakers.

Stereo Irrelevance
A portion of a stereo audio signal which does not contribute to spatial perception. See also: Intensity Stereo.

Stereoisomerism
These are molecules with the same structural formula but their atoms have different positions in space. See also: Enantiomers, Isometry, Racemic Mixture, Structural Isomerism.

Stereoscopic
Pertaining to the use of binocular vision for observation of a pair of overlapping photographs or other perspective views, giving impression of depth.

Stiction
Stiction can be defined as a form of friction which is resistance to the start of movement as opposed to breakage' friction which is resistance to movement after the motion has started. Stiction in the dampers (suspension) is often the cause of the phenomenon known as 'locked up'. See also: Static Friction.

Stiffness
Stiffness is the ratio of change of force (or torque) to the corresponding change in translation (or rotational) deflection of an elastic element. Stiffness is often defined with respect to static or dynamic loading conditions.When a force is applied to a structure, there is a displacement in the direction of the force; stiffness is the ratio of th…

Stilling Well
A cylinder installed near a body of water is used to hold and protect hydrological sensors. The stilling well allows water to move in and out freely but dampens wave and current action so as to provide a reasonable representation of the level of the water body.

Stimulated Emission
The emission of a photon from an atom due to the presence of an incident photon. The emitted photon has the same energy, direction, and phase as the incident photon. See also: Laser, Photons.

Stirling Engine
An external combustion engine. Also known as a Hot Air Engine.The Stirling engine was invented in 1816 by a Scotch clergyman, Robert Stirling, as a competing technology to the steam engine.Stirling engines work by subsequently heating and cooling a gas inside a closed volume. As the gas is heated it expands and as it is cooled it contracts. This …

Stochastic Process
That which maintains a statistically random distribution.

Stoichiometry
Ratios of atoms in a compound.Ratios of moles of compounds in a reaction.A branch of chemistry that quantitatively relates amounts of elements and compounds involved in chemical reactions, based on the law of conservation of mass and the law of definite proportions.

Stokes
The CGS unit of kinematic viscosity. Abbreviated as St. 1St=1x10^-4m²s^-1. See also: Kinematic Viscosity, Viscosity.

Stone
The stone is an old British unit of mass. Traditionally used to express the weight ofa person.Conversions16 ounces (oz)=1 pound (lb)1 stone=14 pounds (lb)1 stone=6.350293 kg1 ton=1016.047 kgttle='Mass';xiunt='kg';yiunt='stone';mconv=6.350293;cconv=0.0; See also: Mass, Pound.

Straight Line
A straight set of points that continue on to infinity in both directions. A straight line on the xy plane is defined by the equation:wherem = gradientc = intercept on y-axisWhen fitting a straight line to a set of experimental data the following may be applied to calculate the gradient (m) and y-axis intercept (c).

Strain
When a structure or component is subjected to stress individual fibres or elements in the material either lengthen or shorten. Strain is a measure of how much these elements extend or contract, and is defined as the change in length divided by the original length of the element. Strains can be defined at a point if the strained element is considere…

Strain Energy
Elastic energy stored in a body which has been deformed by internal or external force. See also: Strain.

Strain Gauge
A sensor that experiences a change in resistance when it is stretched or strained. It is attached to the body subjected to the strain. See also: Strain.

Strain Hardening
An increase in hardness and strength caused by plastic deformation at temperatures lower thanthe recrystallization range.

Strange
The flavor of the third quark. See also: Quark, Strange Particle, Top.

Strange Particle
A particle with a nonzero value of strangeness. In the quark model it is made up of one or more quarks carrying the quantum property of strangeness. See also: Quark, Strange.

Stratified Fluid
In a stratified fluid the density varies with depth. Such circumstances occur naturally, for example, due to variations in temperature in the atmosphere, and due to temperature and salinity variations in the ocean.

Strength
This relates to the maximum force which can be applied to a material without it breaking.In a material, strength refers to a level of stress at which there is a significant change in the state of the material, e.g., yielding or rupture.In a structure, strength refers to a level of level of loading which produces a significant change in the state of…

Stress
Defined as the force per unit area of cross-section.wheres = stress [Nm^-2]F = force [N]A = cross-sectional area [m²]

Stress Relieving
Heating to a suitable temperature, holding long enough to reduce residual stresses and thencooling slowly enough to minimize the development of new residual stresses.

Stress Resultant
A system of forces which is statically equivalent to a stress distribution over an area. See also: Stress.

Stroke
The distance a piston travels up or down inside the cylinder. See also: Bore, Internal Combustion Engine, Piston.

Strong Force
The force responsible for holding the nucleons together to form nuclei. This force reacts only over extremely small distances, of order the size of the nucleus, becoming negligible at distances greater than 10^-15m. The strong force acts on protons and neutrons but not on electrons, neutrinos or photons. The strong force is 137 times stro…

Strontium
Strontium is a soft white metal which can be obtained by the high temperature reduction of SrO by Al, or by the electrolysis of the fused halide (a technique which can be used for the alkali group of metals). It has an abundance in the earth`s crust of 370 ppm and is found naturally in celestine (strontium sulphate) and strontianite (strontium carb…

Strouhal Number
A dimensionless unit.whereS = Strouhal Numberf = frequency [Hz]D = hydraulic dimension [m]V = velocity [ms^-1]

Structural Acoustic Coupling
The physics relating to the vibration of a panel and the sound radiated from it or the acoustic excitation excitation of the panel.

Structural Formula
A formula which shows the arrangement of the atoms in a molecule. See also: Atom, Molecular Formula, Molecule.

Structural Isomerism
These are molecules with the same molecular formula but with different structural arrangements of atoms. See also: Isometry, Stereoisomerism.

Structural Model
An idealization for analysis purposes of a real or conceived structure. A structural model includes boundaries limiting the scope of the analysis. Supports occur at these boundaries, representing things which hold the structure in place.

Structure-Borne Sound
Sound for which a significant portion of the transmission path from source to receiver takes place in a solid structure rather than through a liquid or gas.

Stud
A fastener which is threaded at both ends with an unthreaded shank in between. See also: Thread.

Student's t Distribution
A probability distribution which is very similar in shape to the standard normal distribution. The mean of the t distribution is always equal to 0, while the standard deviation is usually slightly greater than 1. Only one parameter, called the degrees of freedom, is necessary to completely specify the distribution.Values of Student's t are frequent…

Subatomic Erosion
A process in which structures on an integrated circuit's substrate are eroded by the flow of electrons in much the same way as land is eroded by a river.

Subcritical
A chain reaction that dies out because an average of less than one neutron from each fission reaction causes another fission reaction. See also: Supercritical.

Subharmonic
Sinusoidal quantity of a frequency that is anintegral submultiple of a fundamental frequency. See also: Frequency, Harmonic, Subsynchronous.

Subjects
AerodynamicsAerodynamics ConversionsAerodynamics CalculationsAerodynamics BooksAerodynamics Web LinksAerodynamics Source Code Architectural AcousticsArchitectural Acoustics ConversionsArchitectural Acoustics CalculationsArchitectural Acoustics BooksArchitectural Acoustics Web LinksArchitectural Acoustics Source Code AstronomyAstronomy ConversionsA…

Sublimation
The transition of a substance directly from the solid phase to the vapour phase, or in reverse, without going through the liquid phase. See also: Phase Change.

Subset
A subset of a given set is a collection of things that belong to the original set. Every element of the subset must belong to the original set, but not every element of the original set need be in a subset (otherwise, a subset would always be identical to the set it came from).

Subsonic
Having a speed less than that of sound in a designated medium. See also: Hypersonic, Hypervelocity, Mach Number, Sound, Supersonic.

Subsynchronous
Component of a vibration signal that has a frequency less than shaft rotation frequency. See also: Frequency, Fundamental, Harmonic, Subharmonic.

Subtraction
Symbol : -The binary operation of finding the difference between two quantities. In arithmetic, subtraction is not commutative, i.e. , nor associative, .The identity element is 0 only when it is on the right hand side, i.e. .

Subtrahend
A number that is to be subtracted from another number. See also: Minuend, Subtraction.