mu

Look up Μ or μ in Wiktionary, the free dictionary.

Greek alphabet
Αα	Alpha	Νν	Nu
Ββ	Beta	Ξξ	Xi
Γγ	Gamma	Οο	Omicron
Δδ	Delta	Ππ	Pi
Εε	Epsilon	Ρρ	Rho
Ζζ	Zeta	Σσς	Sigma
Ηη	Eta	Ττ	Tau
Θθ	Theta	Υυ	Upsilon
Ιι	Iota	Φφ	Phi
Κκ	Kappa	Χχ	Chi
Λλ	Lambda	Ψψ	Psi
Μμ	Mu	Ωω	Omega
History
Archaic local variants  ·  ·  ·  ·  ·
Ligatures (ϛ, ȣ, ϗ) · Diacritics
Numerals: (6) · (90) · (900)
In other languages
Bactrian  · Coptic  · Albanian
Scientific symbols
Book  · Category · Commons view talk edit

Mu (uppercase Μ, lowercase μ; Ancient Greek μῦ [mŷː]), Modern Greek μι or μυ [mi]) is the 12th letter of the Greek alphabet. In the system of Greek numerals it has a value of 40. Mu was derived from the Egyptian hieroglyphic symbol for water (𓈖) which had been simplified by the Phoenicians and named after their word for water, to become 𐤌. Letters that arose from mu include the Roman M and the Cyrillic М.

Names

Ancient Greek

In Ancient Greek, the name of the letter is written μῦ and pronounced [mŷː].

Modern Greek

In Modern Greek, the name of the letter is spelled μι and pronounced [mi]. In monotonic orthography, the ancient version is written with an acute accent instead of a circumflex: μύ.

Symbol

The lower-case letter mu (μ) is used as a special symbol in many academic fields. The upper case mu is not used, since it is normally identical to Latin M.

Mathematics

In mathematics:

• the µ-roots of a complex number z = a + bi
• the Möbius function in number theory
• the integrating factor in ordinary differential equations
• the population mean or expected value in probability and statistics
• a measure in measure theory
• minimalization in computability theory and Recursion theory
• the learning rate as used in artificial neural networks
• represents the mean in the Normal Distribution

Measurement

In measurement:

• the SI prefix micro-, which represents one millionth, or 10⁻⁶.
• the micron, an old unit which corresponds to the micrometre (which is now denoted "µm")

Physics and engineering

In classical physics and engineering:

• the coefficient of friction (also used in aviation as braking coefficient)
• reduced mass in the two-body problem
• linear density or mass per unit length in strings and other one-dimensional objects.
• permeability in electromagnetism
• the magnetic dipole moment of a current-carrying coil
• dynamic viscosity in fluid mechanics
• the amplification factor or voltage gain of a triode vacuum tube^[1]
• the electrical mobility of a charged particle
• the airspeed relative to rotor tip speed, in rotorcraft

In particle physics:

• the elementary particles called the muon and antimuon

In thermodynamics:

• the chemical potential of a system or component of a system.

Chemistry

In chemistry:

• the prefix given in IUPAC nomenclature for a bridging ligand.

Pharmacology

In pharmacology:

• an important opiate receptor

Orbital mechanics

In orbital mechanics:

• Standard gravitational parameter of a celestial body, the product of the gravitational constant G and the mass M.
• planetary discriminant, represents an experimental measure of the actual degree of cleanliness of the orbital zone, a criterion for defining a planet. µ is calculated by dividing the mass of the candidate body by the total mass of the other objects that share its orbital zone.

Music

• Mu major chord

Software

In application names:

• μTorrent, a BitTorrent client

Cameras

The Olympus Corporation manufactures a series of digital cameras called Olympus µ[mju:] or Olympus Stylus.^[2]

Linguistics

In phonology, it often stands for mora.

Computing

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In Unicode, the upper and lower case mu are encoded at U+039C and U+03BC respectively^[3]. In ISO 8859-7 they are encoded at CC_HEX and EC_HEX. In HTML code, the μ character is represented by "μ", "μ" and the entity "μ".

The micro sign or micron is considered a distinct character from the Greek alphabet letter by Unicode for historical reasons (although it is a homoglyph) and is found at U+00B5 as well as position B5_HEX in ISO 8859-1, 3, 8, 9, 13 and 15, and thus in the corresponding Windows code pages Windows-1252 etc. In HTML code, the µ symbol is represented by "µ", "µ" and the entity "µ". When Alt-0181 or the DOS legacy Alt+230 is typed into an editable field using the numeric keypad in Microsoft Windows, the µ symbol appears. Also pressing AltGr + M results in a µ on some keyboard layouts.

Because µ is the abbreviation for the metric system prefix micro-, the symbol is used in many word plays about the field of micro-computing. For example, the symbol is used in the name and logo of the popular bittorrent client, µTorrent. Also, the microcontrollers are commonly represented in schematics as µC. It is sometimes simply substituted with a u, the most similar-looking ASCII glyph, e.g. uTorrent.

References