### Q factor

**(quality factor)**
(measure of oscillator's damping)

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 more 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 dissipates
too much energy to carry out even a single oscillation, and the
higher the number (1, 100, 1,000,000, etc.), the more oscillations
result without addition of energy.

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**, aka
**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*.

(*physics,resonance,orbits,celestial mechanics*)
http://en.wikipedia.org/wiki/Q_factor

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