Hearing the shape of a rod by the sound of its collision
Francesca M. F. Mascarenhas, C. M. Spillmann, John F. Lindner, Donna Jacobs · American Journal of Physics · 1998
We collide rods of different lengths and infer the vibrational motion of the longer rod by a spectral analysis of the resulting sound. Collisions of rods of square and circular cross sections are audibly different. While longitudinal modes of vibration do not discriminate between different cross-sectional shapes, flexural modes do, and these enable us to hear the shapes of the rods. We use a microphone, an amplifier, and a spectrum analyzer to observe the longitudinal and flexural modes of the ringing rod. With an accessible mathematical model and a simple apparatus, we obtain good agreement between theory and experiment.