Measuring anharmonicity in a large amplitude pendulum

We investigate the anharmonicity of a large amplitude pendulum and develop a novel technique to detect the high Fourier components as a function of the amplitude for large amplitudes close to 180°. The technique involves doing a Fourier analysis on each half-cycle of the amplitude versus time. The presence of the third and fifth harmonics is detected and the variations of the corresponding Fourier coefficients with amplitude are studied. The experimental setup is inexpensive and simple to implement.