  In this paper we present a study of the non-linear effects of anharmonicity
of the potential of the simple pendulum. In a theoretical reminder we highlight
that anharmonicity of the potential generates additional harmonics and the
non-isochronism of oscillations. These phenomena are all the more important as
we move away from the oscillations at small angles, which represent the domain
of validity of the harmonic approximation. The measurement is apprehended by
means of the acquisition box SYSAM-SP5 coupled with the Latis pro software and
the Eurosmart pendulum. We show that only a detailed analysis by fitting the
recorded curve can provide sufficient accuracy to describe the quadratic
evolution of the period as a function of the amplitude of the oscillations. We
we can detect the additional harmonics in the oscillations when the amplitude
becomes very high.
