# constant of proportionality

Noun 1. constant of proportionality - the constant value of the ratio of two proportional quantities x and y; usually written y = kx, where k is the factor of proportionality
factor of proportionality
constant - a number representing a quantity assumed to have a fixed value in a specified mathematical context; "the velocity of light is a constant"
Planck's constant, h - the constant of proportionality relating the energy of a photon to its frequency; approximately 6.626 x 10^-34 joule-second
factor - any of the numbers (or symbols) that form a product when multiplied together. [Based on WordNet 3.0, Farlex clipart collection. © 2003-2012 Princeton University, Farlex Inc.]

"In mathematics, two variables are proportional if a change in one is always accompanied by a change in the other, and if the changes are always related by use of a constant. The constant is called the coefficient of proportionality or proportionality constant.

• If one variable is always the product of the other and a constant, the two are said to be directly proportional. x and y are directly proportional if the ratio y/x is constant.
• If the product of the two variables is always equal to a constant, the two are said to be inversely proportional. x and y are inversely proportional if the product x/y is constant.
• If a linear function transforms 0, a and b into 0, c and d, and if the product a b c d is not zero, we say a and b are proportional to c and d. An equality of two ratios such as a/c = b/d, where no term is zero, is called a proportion." Wikipedia, Proportionality