Inject Noise to start oscillations (shake circuit/device).
This circuit uses feedback to oscillate at its natural/resonant frequency. The output of the amplifier is fed back to both inputs and will only oscillate at a frequency that is in phase at both inputs.
The gain must be >= 3 as the signal is 1/3 at the input.
The circuit and information about it can be found at: http://www.electronics-tutorials.ws/oscillator/wien_bridge.html
