Ra

Ra
Radium is a radioactive element of the alkaline earth metals. White in colour and properties close to barium.
Rabbet
The portion of a doorframe into which the door fits.
RAC Horsepower Rating
An obsolete engine horsepower rating system that was used as a designation as to the power of an engine.
Racemic Mixture
A mixture that has equal amounts of left- and right-handed enantiomers of a chiral molecule.
Racing Line
An imaginary line around a circuit that provides the quickest lap time.
Rack and Pinion
A pair of gears which convert rotational motion into linear motion.
Rack and Pinion Steering
The most common steering system on passenger cars.
Racking
The distortion of a rectangular shape to a skewed parallelogram.
Racon
A transponder for interrogation by a primary radar.
rad
An abbreviation of radian the SI unit of plane angle.
Rad
The rad is a unit used to measure absorbed radiation dose.
Radar
A method, system, or technique of using beamed, reflected, and timed radio waves for detecting, locating, or tracking objects.
Radar Altimeter
Airborne radar that measures the distance of the aircraft above the ground.
Radar Beam
The space in front of a radar antenna where a target can be effectively detected or tracked.
Radar Detector
A detector that, in its simplest form, only needs to be capable of producing an output when RF energy is present at its input.
Radar Mile
Time interval, 12.36 microseconds, for RF energy to travel out from a radar to a target and back to the radar.
Radial
A direction perpendicular to the centreline of a shaft.
Radial Engine
An engine with a number of cylinder arranged in a circle around the crankshaft centre line. A design often used for aircraft engines.
Radial Force Variation
Radial Force Variation is a dynamic force generated at the wheel due to tyre non-uniformity.
Radial Motion
Motion along a radius, or a component in such a direction.
Radial Position
The average location, relative to the radial bearing centreline, of the shaft′s dynamic motion.
Radial Vibration
Shaft dynamic motion or casing vibration which is in a direction perpendicular to the shaft centerline.
Radian
The radian is the plane angle between two radii of a circle which cut off on the circumference an arc equal in length to the radius.
Radian per Second
A common unit of angular velocity.
Radiancy
The rate of radiant-energy emission for a unit area of a source in all the radial directions of the overspreading hemisphere.
Radiant Exposure
The total energy per unit area incident upon a given surface.
Radiant Heating
Heating system in which warm or hot surfaces are used to radiate heat into the space to be conditioned.
Radiant Intensity
Energy of radiation striking a unit area per unit time.
Radiant Panel Test
Used to measure and compare the surface flammability of materials when exposed to a prescribed level of radiant heat energy.
Radiated Noise
The dissemination of sound energy as acoustic waves from a source (e.g. a vibrating panel, running engine etc.).
Radiation
This is the electromagnetic radiation emitted by a body as a function of its temperature.
Radiation Absorbed Dose
The rad is a unit used to measure absorbed radiation dose.
Radiation Belt
An envelope of charged particles trapped in the magnetic field of a spatial body.
Radiation Field
The electromagnetic field that radiates from an antenna and travels through space.
Radiation Intensity
Another name for Radiant Intensity.
Radiation Losses
The losses that occur when magnetic lines of force about a conductor are projected into space as radiation and are not returned to the conductor as the cycle alternates.
Radiation Pattern
A plot of the radiated energy from an antenna.
Radiation Resistance
The resistance that if inserted in place of the antenna would consume the same amount of power as that radiated by the antenna.
Radiator
A device that cools the liquid in the cooling system by allowing it to circulate through a series of water channels, which are exposed to air ducts
Radiator Fan
A fan to provide cooling air toward the radiator.
Radical Axis
The locus of points of equal power with respect to two circle.
Radical Centre
The radical centre of three circles is the common point of interesection of the radical axes of each pair of circles.
Radii
Plural of radius.
Radio
Communication by electromagnetic waves, without a connecting wire.
Radio Clock
A clock that automatically synchronizes to a signal received by radio.
Radio Direction Finder
An instrument that intercepts and uses electromagnetic radiation in the radio portion of the spectrum to determine the direction of the radio transmitter.
Radio Frequency
Any frequency of electromagnetic energy capable of propagation into space.
Radio Frequency Choke
A choke coil with a high impedance at radio frequencies.
Radio Frequency Heating
A process for heating plasma by transferring energy to ions or electrons using waves generated by an external oscillator at an appropriate frequency, and propagated into the plasma.
Radio Frequency Interference
This is unwanted Electromagnetic Emissions in the radio reception bands.
Radio Frequency Telemetry
A telemetry system that transmits data over a radio frequency.
Radio Horizon
The boundary beyond the natural horizon in which radio waves cannot be propagated over the earth′s surface.
Radio Interference
The interference with radio reception caused by a system.
Radio Interference Suppression
The methods employed to minimize radio interference.
Radio Interferometer
An interferometer operating at radiofrequencies.
Radio Waves
Electromagnetic radiation in the region of the spectrum smaller than about 3 x 108Hz and wavelengths greater than about 1 m.
Radioactive Decay
The spontaneous change of an atomic nucleus accompanied by the emission of alpha, beta particles or gamma radiation.
Radioactivity
Spontaneous emission of particles or high-energy electromagnetic radiation from the nuclei of unstable atoms.
Radioisotope
A radioactive isotope.
Radiometer
Instrument for detecting and measuring radiant energy.
Radiometer Vacuum Gauge
Another name for a Knudsen Gauge.
Radiometry
A branch of science which deals with the measurement of radiation.
Radiosity Equation
Used in the construction of realistically lit scenes in computer graphics.
Radiosonde
A small, expendable, balloon-borne instrument package with a radio transmitter used to measure the air temperature, pressure and humidity of the atmosphere above the earth′s surface.
Radium
A radioactive element of the alkaline earth metals. White in colour and properties close to barium.
Radius
In a circle, the radius is the distance from the centre of the circle to a point on the circle.
Radius Gauge
Any one of a number of small flat, standard-shaped metal leafs or blades used for checking the accuracy of regular concave and convex surfaces.
Radix
The number of distinct symbols used in a number system.
Radix Point
The generalization of decimal point to bases of numeration other than base 10.
Radome
Dielectric housing for an antenna.
Radon
A radioactive element and the heaviest of the nodle gases.
Rafter
A framing member that runs up and down the slope of a pitched roof.
Ragone Plot
A chart used for performance comparison of various energy storing devices.
Rain Bucket
Device for measuring rain fall.
Rain Gauge
Instrument used to measure the total amount of precipitation that falls upon a given unit area during a specified time interval.
Rainflow Analysis
A method of representing a random signal by various numbers of sinusoids that would produce the same amount of fatigue damage.
RAM
Abbreviation of Random Access Memory, a data storage device for which the order of access to different locations does not affect the speed of access, except for bursts.
Ram Air
Air entering an air inlet as a result of the high-speed forward movement.
Ramjet
A jet engine with no mechanical compressor, consisting of specially shaped tubes or ducts open at both ends.
Ramp Voltage
A steadily rising voltage.
Ram-Rocket
A rocket engine in which an air-breathing inlet and duct system are added, permitting atmospheric air to be introduced at the exit of the rocket combustion chamber.
Ramsay, William
Discovered Argon, Krypton and Xenon and independently discovered Helium on earth.
Random Access Memory
A data storage device for which the order of access to different locations does not affect the speed of access, except for bursts.
Random Copolymer
A polymer in which two different mer units are randomly distributed along the molecular chain.
Random Errors
Errors that remain after blunders and systematic errors have been removed.
Random Experiment
An experiment or trial whose outcome is not perfectly predictable, but for which the long-run relative frequency of outcomes of different types in repeated trials is predictable.
Random Noise
A noise signal, commonly used in measurements, which has constantly shifting amplitude, phase, and a uniform spectral distribution of energy.
Random Number Generators
A device used to produce a selection of numbers in a fair manner, in no particular order and with no favour being given to any numbers.
Random Process
A random process is a collection of time-history records that can be described by appropriate statistical parameters, such as averaged properties of these records at a number of fixed times.
Random Sampling
A sampling method in which all elements in the population have an equal chance of being selected.
Random Vibration
A vibration whose instantaneous magnitude is not specified for any given instant of time.
Random Wound Stator
The stator windings are wound onto a bobbin without a defined structure to the windings.
Randomised Controlled Experiment
A controlled experiment in which the assignment of subjects to the treatment group or control group is done at random, eg by drawing straws.
Range
The maximum and minimum allowable full-scale signal.
Range Extender
A device that extends the range of an electric vehicle by converting an energy dense fuel into electricity.
Range of Linear Transformation
The range of a linear transformation T is the set of all vectors T(v), where v is any vector in its domain.
Rankine Cycle
A mathematical model that is used to predict the performance of steam engines. The Rankine cycle is an idealised thermodynamic cycle of a heat engine that converts heat into mechanical work. The heat is supplied externally to a closed loop, which usually uses water as the working fluid.
Rankine Temperature Scale
An absolute scale of temperature based on degrees Farenheit.
Rankine Vortex
An idealized vortex in unbounded fluid with uniform vorticity inside a circular patch and zero vorticity outside.
Rankine-Hugoniot Shock Relations
These are solutions for a steady, normal shock in the frame moving with the shock front.
Raoult′s Law
The vapour pressure of a solvent in an ideal solution equals the mole fraction of the solvent times the vapour pressure of the pure solvent.
Rapid Solidification Technology
Process in which molten metals such as titanium and aluminum are transformed into a very fine powder, which is then solidified.
Rapid Speech Transmission Index
Abbreviated as RASTI and expressed in a decimal range of 0.2 for "bad" to 1.00 for "Excellent".
Rare Earth
An oxide of a rare earth element.
Rare Earth Element
A metallic element that belongs to Group 3B or to the lanthanide series.
Rarefaction
A decrease in density and pressure in a medium, such as air, caused by the passage of a sound wave.
Rarefied Wave
A longitudinal wave that has been expanded or rarefied as it moves away from the source.
Rasp
A sort of blowing noise emitted often from the exhaust pipes of internal combustion engines, usually, it is dominated by a mixture of 4E, 6E and 8E engine orders on 4 cylinder engines.
RASTI
Rapid Speech Transmission Index, expressed in a decimal range of 0.2 for "bad" to 1.00 for "Excellent".
Ratchet
A mechanism that only allows rotary motion in one direction.
Ratchet Brace
A brace that includes a ratchet for ease of use in tight spaces, and also to use just the most powerful or easiest arc of turn.
Rate Gyroscope
A gyroscope used to detect and measure angular rates of change.
Rate Law
A rate law or rate equation relates reaction rate with the concentrations of reactants, catalysts, and inhibitors.
Rate of Change
The speed at which a function is changing.
Rate of Reaction
The rate at which the concentration of a product increases or the concentration of a reactant decreases with time.
Rate of Strain Hardening
Alternative name for Modulus of Strain Hardening.
Rated Flow
The maximum flow that the power supply system is capable of maintaining at a specific operating pressure.
Rated Pressure
The qualified operating pressure which is recommended for a component or a system by the manufacturer.
Ratio
The quotient of two numbers.
Ratio Detector
A detector that uses a double-tuned transformer to convert the instantaneous frequency variations of the FM input signal to instantaneous amplitude variations.
Ratio of Specific Heats
The ratio of molar heat capacity at constant pressure to molar heat capacity at constant volume.
Rational B-Spline
equation that permits the modeling of free-form curves between two endpoints as a function of a set of intermediate points whose values influence the shape of the curve.
Rational Function
Any function which can be defined by a rational fraction, i.e. an algebraic fraction such that both the numerator and the denominator are polynomials.
Rational Number
Any number that can be expressed as the ratio of two integers.
RATO
Utilising solid or liquid fuel rockets to augment the take-off.
Rattle
A sound such as that made when shaking a tin full of coins.
Rawlplug
The inventer of the original wall plug was John Rawlings and he marketed the Rawlplug.
Ray
At higher audio frequencies, sound may be considered to travel in straight lines, in a direction normal to the wave front.
Ray Tracing
The calculation of the propagation, reflection and refraction of rays from source to receiver. This technique is used extensively within the optics and acoustics industry.
Rayl
The Rayl is the SI derived unit of specific acoustic impedance.
Rayleigh Criterion
A criteria that gives an approximation for how finely a set of optics may be able to distinguish.
Rayleigh Distribution
An example is the variation of wave height in a sea where swell is the main component.
Rayleigh Scattering
Scattering of radiation in the course of its passage through a medium containing particles, the sizes of which are small compared with the wavelength of the radiation.
Rayleigh Waves
These are also known as surface waves.
Rayleigh-Jeans Law
A law describing blackbody radiation.
Rayleigh′s Method
A method used for calculating approximate natural frequencies for a vibrating system assuming a deflected shape and balancing kinetic and strain energies.