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# Mu (Μ, μ) Definition

Mu (Μ, μ) or my 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, which had been simplified by the Phoenicians and named after their word for water, to become (mem). Letters that derive from mu include the Roman M and the Cyrillic М.

## Usage in Mathematics & Science

The lowercase letter mu (μ) is used as a special symbol in many academic fields. Uppercase mu is not used, because it appears identical to Latin M.

The lowercase Mu (μ) is used for:

• Measurement:

• The SI prefix micro, which represents one millionth, or 10-6. Lowercase letter u is often substituted for μ when the Greek character is not typographically available; for example the unit microfarad, correctly μF, is often rendered as uF or ufarad in technical documents.

• The micron μ, an old unit now named the micrometer and denoted μm.

• Mathematics:

• μ is conventionally used to denote certain things; however, any Greek letter or other symbol may be used freely as a variable name.

• A measure in measure theory.

• Minimalization in computability theory and Recursion theory.

• The integrating factor in ordinary differential equations.

• The learning rate in artificial neural networks.

• The degree of membership in a fuzzy set.

• The Möbius function in number theory.

• The population mean or expected value in probability and statistics.

• The Ramanujan–Soldner constant.

• Physics & Engineering:

• The coefficient of friction (also used in aviation as braking coefficient).

• Reduced mass in the two-body problem.

• Standard gravitational parameter in celestial mechanics.

• 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.

• The electrical mobility of a charged particle.

• The rotor advance ratio, the ratio of aircraft airspeed to rotor tip speed in rotorcraft.

• Chemistry:

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

• Biology:

• The mutation rate in population genetics.

• Pharmacology:

• An important opiate receptor.

• 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. The value of 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.

• Electronic musician Mike Paradinas runs the label Planet Mu which utilizes the letter as its logo, and releases music under the pseudonym μ-Ziq, pronounced music.

• Used as the name of the school idol group μ's, pronounced muse, consisting of nine singing idols in the anime Love Live! School Idol Project.

• Official fandom name of Kpop group f(x), appearing as either MeU or μ.

## Greek Alphabet

The letters of the Ancient Greek Alphabet, which are frequently utilized in math and science:

 Greek Alphabet Symbol Letter Symbol Letter Uppercase Lowercase Uppercase Lowercase Α α Alpha Ν ν Nu Β β Beta Ξ ξ Xi Γ γ Gamma Ο ο Omicron Δ δ Delta Π π Pi Ε ε Epsilon Ρ ρ Rho Ζ ζ Zeta Σ σ Sigma Η η Eta Τ τ Tau Θ θ Theta Υ υ Upsilon Ι ι Iota Φ φ Phi Κ κ Kappa Χ χ Chi Λ λ Lambda Ψ ψ Psi Μ μ Mu Ω ω Omega

### Sources

“Mu (Letter).” Wikipedia, Wikimedia Foundation, 12 Apr. 2020, en.wikipedia.org/wiki/Mu_(letter).

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