本文利用智能手机内置传感器与Phyphox软件，探究了简谐振动的周期公式和耦合双自由度振动的规律，测量了多自由度振动系统（人行天桥）的固有频率. 实验结果表明，用手机和Phyphox得出的简谐振动周期公式与理论公式非常接近. 对双自由度系统，验证了简正模思想在分析耦合振动系统是可行的. 对于桥梁这样复杂的多自由度振动系统，运用手机就可以很方便地测量其固有频率.

The period formula of simple harmonic vibration and the law of coupled two-degree freedom vibration are explored by using the built-in sensor of smart phone and the APP of Phyphox, and the natural frequency of multi- degree freedom vibration system (pedestrian bridge) is also measured. The experiment results show that the period formula of simple harmonic vibration obtained by mobile phone and Phyphox is very close to the theoretical formula. For two-degree freedom system, it is verified that the idea of normal- model is feasible in the analysis of coupled vibration system. For the bridge such a complex multi-degree freedom vibration system, the use of mobile phones can be very convenient to obtain its natural frequency.