Stigma (letter) Stigma (letter) Stigma (ϛ) is a ligature of the Greek letters sigma (Σ) and tau (Τ), which was used in writing Greek between the Middle Ages and the 19th century. It is also used as a numeral symbol for the number 6. In this unrelated function, it is a continuation of the old letter digamma (originally Ϝ, cursive form ), which had served as a numeral since antiquity and was conflated with the σ-τ ligature in the minuscule handwriting of the Middle Ages. The στ ligature (, ) was one of many ligature forms that came into widespread use as
Torque the definition used in US physics in its usage of the word "torque". In the UK and in US mechanical engineering, torque is referred to as "moment of force", usually shortened to "moment". In US physics and UK physics terminology these terms are interchangeable, unlike in US mechanical engineering, where the term "torque" is used for the closely related "resultant moment of a couple". "Torque" is defined mathematically as the rate of change of angular momentum of an object. The definition of torque states that one or both of the angular velocity or the moment of inertia of an object