教材示例几乎都使用固有频率表达式不显含弹簧静变形的例子，但确实存在相反的情形。针对单自由度振动系统，研究了弹簧静变形从固有频率表达式中消失的充要条件。笔者采用了能使广义质量为常数的广义坐标，从而只用研究系统的势能。研究发现静变形消失的充要条件是：在静平衡位置弹簧轴线与其运动端点的轨迹相切，且以弹簧运动端点位移为广义坐标所得到广义质量对广义坐标的导数应为0。

Nearly all of examples in vibration textbooks are characterized by the intrinsic frequency not implicated by the spring's static deformation. However，there exist indeed counter examples. We consider the case of the single-degree-of-freedom system and investigate its if-and-only-if conditions for the spring's static deformation vanishing from the intrinsic frequency expression. The generalized coordinates rendering a constant generalized mass are used，consequently，only the potential energy is analyzed. After systematically theoretical analysis，we find that the vanishing conditions pertain to parameters of the static balance position ( SBP) . The if-and-only-if conditions are that，firstly，the spring axis must be tangential to its moving end trajectory at the SBP，and secondly，if the displacement arc of the spring moving end is chosen as the generalized coordinate，the derivative of the generalized mass with respect to the arc coordinate must be zero at the SBP.