摘要
Statically indeterminate systems are experimentally demonstrated to be in fact dynamical. Take the classic problems of a beam with three supporting points, granules in a silo, and a ladder leaning against a wall, for instance; their reaction forces are found to vary logarithmically for over 104s with an increment or decrement of more than 10%. This seemingly contradictory mixture of dynamics for a static system is shown to derive from the evolution of microcontact area with the ground and/or wall due to the aging effect.