Universal Time (UT) is a timescale based on the rotation of the Earth. It is a modern continuation of the Greenwich Mean Time (GMT), i.e., the mean solar time on the meridian of Greenwich, England, which is the conventional 0-meridian for geographic longitude. GMT is sometimes used, incorrectly, as a synonym for UTC. The old GMT has been split, in effect into UTC and UT1.
Universal Time - Universal Time and standard time.
Prior to the introduction of standard time, every municipality set its clock, i ...
A barn (symbol b) is a unit of area. While the barn is not an SI unit, it is accepted (although discouraged) for use with the SI. It is used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions. A barn is approximately equal to the area of a uranium nucleus.
Barn unit - Definition.
1 barn (b) = 10−28 square metres (m²)
Barn unit - Commonly used prefixed versions.
The picobarn (pb) = 10−40 m² i ...
The International Bureau of Weights and Measures is the English name of the Bureau international des poids et mesures (BIPM, often written in English Bureau International des Poids et Mesures), a standards organization, one of the three organizations established to maintain the International System of Units (SI) under the terms of the Convention du Mètre (Metre Convention). Note that the abbreviation IBWM does not exist.
It is based at th ...
A byte is commonly used as a unit of storage measurement in computers, regardless of the type of data being stored. It is also one of the basic integral data types in many programming languages.
Byte - Meanings.
The word "byte" has several meanings, all closely related:
A contiguous sequence of a fixed number of bits. On modern computers, an eight-bit byte or octet is by far the most common. This was not always the case. Certain older models have used six-, seven-, or nine- ...
The Boltzmann constant (k or kB) is the physical constant relating temperature to energy.
It is named after the Austrian physicist Ludwig Boltzmann, who made important contributions to the theory of statistical mechanics, in which this constant plays a crucial role. Its experimentally determined value (in SI units, 2002 CODATA value) is:
k = 1.380 6505(24) × 10−23 ...
SI units were used where possible. Unless otherwise stated, standard conditions were used.
Disclaimer and references
Benzoyl peroxide is a chemical in the organic peroxide family. It consists of two benzoyl groups (benzaldehyde with the H of CHO removed) joined by a peroxide group.
Benzoyl peroxide - Precautions.
Benzoyl peroxide, like most peroxides, is a powerful bleaching agent. Contact with fabric (including clothing and bed linens) or hair can cause permanen ...
General
Physical
Thermochemistry
Safety
SI units were used where possible. Unless otherwise stated, standard conditions were used.
Disclaimer and references
Benzalkonium Chloride is an organic compound that is used as an antiseptic and spermicide. This product is a nitrogenous cationic surface-acting agent belonging to the quaternary ammonium group. Benzalkonium chloride is a mixture of alkylbenzyl dimethylammonium chlorides of various alkyl chain lengths. The greatest bactericida ...
The second moment of area, also known as the second moment of inertia and the area moment of inertia, is a property of a shape that is used to predict its resistance to bending and deflection.
It is derived with use of the parallel axes rule. The second moment of area is not the same thing as the moment of inertia, which is used to calculate angular acceleration.
Second moment of area - Definition.
Ix - the moment of inertia about the axis < ...
General
Physical
Thermochemistry
Safety
SI units were used where possible. Unless otherwise stated, standard conditions were used.
Disclaimer and references
Ammonium perchlorate is a chemical compound with the formula NH4ClO4. It is the salt of ammonia and perchloric acid. Like other perchlorates, it is a powerful oxidizer.
This salt is used as an explosive in mining, due to th ...
Heat (also improperly called heat change) is a transient form of energy. It quantifies the spontaneous transfer of thermal energy due to a temperature gradient. The SI unit for heat is the joule.
Heat is a process quantity --as opposed to being a state quantity--, and is to thermal energy as work is to mechanical energy. Heat flows between regions that are not in thermal equilibrium with each other; it spontaneously flows from areas of high temperature to areas of low temperature. All objects (matter) have a certain amou ...
H is the eighth letter of the Latin alphabet. Its name in English is aitch.
In the International Phonetic Alphabet, this symbol is used to represent two sounds. Its lowercase form, [h], represents the voiceless glottal fricative, and its small capital form, [ʜ], represents the voiceless epiglottal fricative.
H - History.
The Semitic letter ח (khêt) probably represented the voic ...
G is the seventh letter in the Roman alphabet. Its name in English is gee.
G - History.
The letter G was created by the Romans because they felt that C was not an adequate letter to represent both /k/ and /g/.
The alleged inventor is a known historical figure, Spurius Carvilius Ruga (who flourished around 230 BC). G, which at this time took the place in the alphabet formerly held by Z, came to represent the sound /g/. As the sound /k/ did, /g/ also developed palatal and velar all ...
The eleventh letter of the Latin alphabet, K, or k comes from the Greek Κ or κ (Kappa) developed from the Semitic Kap, symbol for an open hand. The Semitic soundish value /k/ was maintained in most Classic as well as Modern Languages, although Latin abandoned K almost completely, preferring C. Therefore, the Romance languages have K only in foreign words. Its name in English is kay.
In the International phonetic alphabet, [k] is the symbol for the voiceless velar plosive.
K - Alternative re ...
The month is a unit of time, used with calendars, which is approximately as long as some natural period related to the motion of the Moon. The traditional concept arose with the cycle of moon phases; such months (lunations) are synodic months and last ~29.53 days. From excavated tally sticks, researchers have deduced that people counted days in relation to the Moon's phases as early as the Paleolithic age. Synodic months are still the basis of many calendars.
Month - Astronomical background.
The moti ...
In physics, a magnetic field is an entity produced by moving electric charges (electric currents) that exerts a force on other moving charges. (The quantum-mechanical spin of a particle produces magnetic fields and is acted on by them as though it were a current; this accounts for the fields produced by "permanent" ferromagnets.) A magnetic field is a vector field: it associates with every point in space a (pseudo-)vector that may vary in time. The direction of the field is the equilibrium direction of a compass needle placed in the f ...
M is the thirteenth letter of the latin alphabet. Its name in English is em.
M is also the title of a 1931 film by Fritz Lang, and its 1951 remake.
M is also the name of a now-defunct professional videocassette format developed by Matsushita and RCA.
M also is a pop band known from the synthpop hit Pop Muzik.
M - History.
The letter M represents the bilabial nasal consonant sound, IPA [m], in Classi ...
The lux (symbol: lx) is the SI unit of illuminance. It is used in photometry as a measure of the perceived intensity of light.
Lux - Definition.
1 lx = 1 lm/m2 = 1 m2·m–4·cd
Lux - SI multiples.
Lux - Explanation.
It is equal to one lumen per square metre.
sunlight on an average day ranges from 32 000 (32 klx) to 100 000 lux (100 klx)
TV studios are lit at about 1 000 lux (1 klx)
< ...
Viscosity is a measure of the resistance of a fluid to deformation under shear stress. It is commonly perceived as "thickness", or resistance to pouring. Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. Thus, water is "thin", having a low viscosity, while vegetable oil is "thick" having a high viscosity.
Viscosity - Newton's theory.
When a shear stress is applied to a solid body, the body deforms until the deformation results in an opposing forc ...
The letter F is the sixth letter in the Latin alphabet. Its name in English is ef, spelled eff when used as a verb.
On keyboards, often the F and J keys (or occasionally the D and K keys) have a raised dot or bar on their surface, perceptible to the touch, to assist in typing, especially for the blind. All other keys can be found with their relative positions around these two keys as the index finger normally rests on F and J keys (or the middle finger in the case of D and K).
F - Hi ...
A day (symbol: d) is a unit of time equal to 24 hours. It is not an SI unit but it is accepted for use with SI. The SI unit of time is the second.
It has several definitions.
Day - Definition of a day in SI.
A day is defined as 86,400 SI seconds.
times from 10 kiloseconds to 100 kiloseconds, night, Calculating the day of the week, Daylight saving time, season, for a discussion of daylight and darkness near the poles and the equator and places in-between, Dagr, B ...
C (lowercase c) is the third letter of the Roman alphabet. Its name in English is cee.
In the Etruscan language, plosive consonants had no contrastive voicing, so the Greek Γ (Gamma) was used to represent /k/. In the beginning, the Romans used C for both /k/ and /g/, only later adding a horizontal bar at right-center to produce G. It is possible but uncertain that C represented only /g/ at an even earlier time, while K might have been used for /k/.
Some scholars claim that the Semitic ג (gîmel) pictured a camel, but most assume it was probably < ...
A barometer is an instrument used to measure atmospheric pressure.
Barometer - Liquid barometers.
Barometer - Water-based barometers.
This concept of "decreasing pressure means bad weather" is the basis for a primitive weather prediction device called a weather glass or thunder glass. It can also be called a "storm glass" or a "Goethe thermometer" (the writer Goethe popularized it in Germany).
It consists of a glass container with a spout. The container is filled w ...
