Nu /njuː/ (uppercase Ν lowercase ν, also transcribed Ny; modern Greek: Νι Ni), is the 13th letter of the Greek alphabet. In the system of Greek numerals it has a value of 50. It is derived from the Phoenician letter nun . Its Latin equivalent is N, though the lowercase resembles the Roman lowercase v.
The name of the letter is written νῦ in Ancient Greek and traditional Modern Greek polytonic orthography, while in Modern Greek it is written νι .
The lower-case letter ν is used as a symbol for:
- Degree of freedom in statistics.
- The spatial frequency of a wave in physics and other fields.
- The specific volume in thermodynamics.
- Kinematic viscosity in fluid mechanics.
- Poisson's ratio, the ratio of strains perpendicular with and parallel with an applied force.
- Any of three kinds of neutrino in particle physics.
- One of the Greeks in mathematical finance, known as "vega".
- The number of neutrons released per fission of an atom in nuclear physics.
- A DNA polymerase found in higher eukaryotes and implicated in Translesion Synthesis.
- Molecular vibrational mode, νx where x is the number of the vibration (a label).
- The stoichiometric coefficient.
- The Greatest fixed point of a function, as commonly used in the μ-calculus.
- The maximum conditioning possible for an unconditioned stimulus in the Rescorla-Wagner model.
- The true anomaly, it is an angular parameter that defines the position of a body moving along an orbit, see orbital elements.