Abstract: The dynamic equations of three-line pendulum are given, the differential and integral expressions of kinetic energy theorem are derived. The variation curves of rotational kinetic energy and translational kinetic energy changing with angle coordinate are drawn using MATLAB. The influence of translational kinetic energy on the period of vibration is analyzed.

Key words: three-line pendulum, kinetic energy theorem, rotational kinetic energy, translational kinetic energy, period of vibration