从热力学的角度，本文对2018 年国际青年物理学家锦标赛( IYPT2018) 的第三个课题“跳舞的硬币( Dancing Coin) ”进行了理论分析. 该现象与生活密切相关，描述了一个温度非常低的瓶子上一枚硬币所发生的运动，且这样一个热力学系统可作为一个很好的教学案例，让学生对气体的热化、绝热膨胀等相关热力学过程有直观深入的了解. 本文的研究得到硬币弹起时间和系统的热力学量的关系，同时发现，硬币“跳舞”的时间间隔与系统与环境的温差呈负相关，即硬币跳舞的时间间隔随着系统被环境加热而越来越长，直至无法跳起. 进一步研究表明，瓶内气体的初始温度与环境温差越大，最大弹起次数越大; 临界压强与大气压越接近，最大弹起次数越大. 本文最后通过实验验证了所给理论模型中的假设及其预言的正确性.

From the perspective of thermodynamics，this paper conducts a theoretical analysis of the phenomenon of dancing coin，the third question of 2018 IYPT. This phenomenon is closely related to daily life，describes the motion of a coin on the neck of a very cold bottle，and such a thermodynamic system can serve as a good teaching model，enabling students to have an intuitive and in-depth understanding of thermodynamic processes such as gas heating and adiabatic expansion. In this study，the relationship between the bouncing time of the coin with the thermodynamic quantity of the system is obtained. It is found that the time interval of the coin dancing is negatively correlated with the temperature difference between the system and the environment，that is，the time interval of coin dancing will be longer and longer as a system is heated by the environment，until it could not jump. Further research shows that，the greater the difference between the initial temperature of the gas in the bottle and the ambient temperature，the greater the maximum bouncing time，and the closer the critical pressure is to the atmospheric pressure，the greater the maximum bouncing time. This paper further verifies the reasonability of theoretical hypothesis and the results deduced from theoretical analysis through experiments.