(in lingua inglese)
An analytical technique has been presented based on a modified harmonic balance method to determine approximate solutions for the strongly nonlinear equation which comes from the motion of rigid rod on the circular surface without slipping. In comparison with the previously published methods, determination of solutions is straightforward and simple. The high accuracy and validity of approximate solutions assured us about the solution and reveal that these methods can be used for nonlinear oscillators even with higher order of nonlinearity