Free vibration: a kind of vibration caused by initial excitation (usually pulse force);
Simple harmonic vibration: the vibration waveform is a single sine wave;
Damped vibration: vibration whose amplitude gradually decreases with time due to friction, medium resistance or other energy consumption, and free vibration is one of them. Most vibration in reality belongs to damping vibration.
Undamped vibration: Contrary to damped vibration, it belongs to an ideal state.
Forced vibration: Contrary to free vibration, it refers to the vibration generated by external force that changes continuously and periodically, such as swinging.