本文分析重力对竖直振动的影响．应用Lagrange方程研究多自由度定常保守线性系统，若重力势能为广义坐标的线性函数，则以静平衡位形为坐标原点，重力被静变形效应抵消而可以忽略. 以单自由度系统竖直方向非线性振动为例，说明重力对线性化系统和非线性项均有影响，不能忽略．研究结果明确了国内外振动教材中相关结论成立的条件．

The effects of the weight on vertical vibrations are analyzed. The Lagrangian equation is applied to a multi-degree-of-freedom time-independent conservative linear systems with the gravitational potential energy as a linear function of generalized coordinates to demonstrate that the weight can be canceled by the static deformation effect and then ignored together provided that the static equilibrium configuration is chosen as the origin the the generalized coordinates. A vertically vibrating one-degree-of-freedom nonlinear system is treated as an example to reveal that the weight changed both the linearized system and the nonlinear terms and thus cannot be ignored. The investigation outcomes clarify the validity conditions of relevant conclusions in domestical and international textbooks on vibrations.