Ra

Ra

Radium is a radioactive element of the alkaline earth metals. White in colour and properties close to barium.

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.

Rack and Pinion

A pair of gears which convert rotational motion into linear motion.

Racking

The distortion of a rectangular shape to a skewed parallelogram.

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.

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 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.

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.

Radii

Plural of radius.

Radio Frequency Choke

A choke coil with a high impedance at radio frequencies.

Radio Frequency Interference

This is unwanted Electromagnetic Emissions in the radio reception bands.

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.

Radiosity Equation

Used in the construction of realistically lit scenes in computer graphics.

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 Point

The generalization of decimal point to bases of numeration other than base 10.

Radon

A radioactive element and the heaviest of the nodle gases.

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.

Ramjet

A jet engine with no mechanical compressor, consisting of specially shaped tubes or ducts open at both ends.

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 Noise

A noise signal, commonly used in measurements, which has constantly shifting amplitude, phase, and a uniform spectral distribution of energy.

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.

Range

The maximum and minimum allowable full-scale signal.

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.

Rapid Speech Transmission Index

Abbreviated as RASTI and expressed in a decimal range of 0.2 for "bad" to 1.00 for "Excellent".

Rarefaction

A decrease in density and pressure in a medium, such as air, caused by the passage of a sound wave.

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.

Rate of Reaction

The rate at which the concentration of a product increases or the concentration of a reactant decreases with time.

Ratio

The quotient of two numbers.

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 Number

Any number that can be expressed as the ratio of two integers.

Rattle

A sound such as that made when shaking a tin full of coins.

Ray

At higher audio frequencies, sound may be considered to travel in straight lines, in a direction normal to the wave front.

Rayl

The Rayl is the SI derived unit of specific acoustic impedance.

Rayleigh Distribution

An example is the variation of wave height in a sea where swell is the main component.

Rayleigh Waves

These are also known as surface waves.

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.