For a pendulum, the period equals this quantity times the square root of length over g.
The bandwidth theorem says that the product of width in the frequency domain and width in the time domain is approximately this number. The Q factor is this quantity times energy stored over energy lost per cycle. Inductive reactance is equal to frequency times inductance times this quantity. For a pendulum, the period equals this quantity times the square root of length over g. The wavenumber is equal to this quantity divided by wavelength, and Planck's constant divided by this value gives the reduced Planck constant. In wave mechanics, a phase shift of any multiple of this quantity is equivalent to the original wave. For 10 points, name this quantity, equal to the number of radians in a circle.
The bandwidth theorem says that the product of width in the frequency domain and width in the time domain is approximately this number.
2π [accept tau, accept equivalents like two times pi, do not accept "pi"]