Moment

In most simplest terms, a moment of a physical quantity is product of the distance to a given point, raised to a power, and the value of that quantity at that point:

A more general definition can be sourced from the theory of probabilities and statistics which deals with density functions and distributions functions (which in turn, are representing some physical quantity). Consider a independent (thus random) variable and a density function (or a distribution function) . In other words, is some quantity which is distributed over . Then, we can write

where is the th moment. When dealing with physical quantities, can have various forms, but the major forms of interest are as follows

1. If represents spatial position, then would yield geometric moments,
2. If represents velocity, then would yield kinetic moments,
3. If represents direction, then would yield angular moments,
4. If represents energy, then would yield spectral moments.