2025/12/15 by Katsuya Shimabukuro, Kosaku Horinaga, Shimabukuro, Katsuya +11
Engineering · Physics and Astronomy · #Advanced Thermodynamics and Statistical Mechanics #Biological Physics (physics.bio-ph) #Biomimetic flight and propulsion mechanisms #FOS: Physical sciences #Micro and Nano Robotics
paper · pdf · doi:10.48550/arxiv.2512.13013
openalex publication_date 2025/12/15 · openalex created_date 2025/12/17 · openalex updated_date 2026/07/28
The transduction of force into motion for microswimmers at intermediate Reynolds numbers (Re ∼ 1), where inertia becomes relevant, is a fundamental problem in active matter. Using the multicellular alga Volvox as a model physical system, we perform the first direct measurements that deconvolve a swimmer's inertial impact force from its motor's propulsive force. We discover a ∼30 Hz propulsive pulse, the mechanical signature of collective ciliary action. This high-frequency motor output drives a fluctuating velocity in the low-Re V. carteri, but is mechanically filtered by the inertia of the larger V. ferrisii, resulting in a smooth swimming trajectory. Our work demonstrates that for swimmers beyond the Stokes regime, kinematics are not a direct proxy for the underlying motor dynamics, a foundational assumption in the study of microscopic motility.