Q factor

The Q factor (quality factor) is a quality of an oscillator reflecting how damped it is, the higher the Q factor, the less damping and the longer the oscillator will resonate. For example, a pendulum's friction lowers its Q factor. The Q factor is defined as:

              energy stored
Q = 2π x ———————————————————————————
         energy dissipated per cycle

The Q factor is scaled so that a factor of 1/2 or less indicates the oscillator will dissipates too much energy to carry out even a single oscillation. The higher the number (1, 100, 1,000,000, etc.), the longer oscillations continue before the oscillator runs out of energy, presuming no additional energy is added during the oscillations.

The Q factor arises in astrophysics, for example, regarding orbital resonances.

A Q factor is used as a measure of some of the effects of tides on orbits and body rotations, called the tidal q factor (tidal Q or tidal quality factor). This is a Q-factor-style measure of the ratio between energy dissipated by an oscillation and a measure of the deformation during an oscillation. Like the above, high tidal Q factors (a thousand, a million) result in very slow damping/dissipation, and lower numbers leading to quicker dissipation. Such a tidal Q factor depends upon the specific oscillation, e.g., a body's tidal deformation due to its rotation under the influence of a nearby mass (e.g., a planet and its host star) has a corresponding tidal Q factor, and if it also undergoes a deformation due to an eccentric orbit, that oscillation has a not-necessarily-the-same tidal Q factor. In other words, a body can be undergoing multiple overlapping oscillations, each with its own Q factor.