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Macroscopic Brownian motion on a chaotic fluid interface.

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Title: Macroscopic Brownian motion on a chaotic fluid interface.
Authors: Barotta, Jack-William1 (AUTHOR) jack-william_barotta@brown.edu, Barotta, Caroline M.2 (AUTHOR), Silver, Eli1 (AUTHOR), Harris, Daniel M.1 (AUTHOR)
Source: American Journal of Physics. Jul2026, Vol. 94 Issue 7, p570-574. 5p.
Subjects: Brownian motion, Surface waves (Fluids), Particle tracking velocimetry, Unsteady flow, Inertia (Mechanics), Liquid-liquid interfaces, Experimental methods in education
Abstract: Brownian motion is the erratic motion of an object due to collisions with the fluid in which it is immersed. In this work, we detail a tabletop laboratory demonstration of underdamped Brownian motion wherein a macroscopic particle resting on a driven fluid interface exhibits ballistic motion at short times and diffusive motion at long times. We observe the trajectory of a centimeter-sized disk driven by a field of chaotic Faraday waves excited by a shaker. The crossover from ballistic to diffusive motion occurs at time and length scales experimentally accessible through particle tracking of a video recorded with a standard phone camera. Along with representative data, we provide a complete assembly guide and operating procedure for students so that the experiment can be readily applied in the classroom. The tabletop setup can also be adapted for other student projects and active research topics relating to particle motion on a vibrating fluid interface. Editor's Note: Normally when students observe Brownian motion in the lab, they have to accept that the crossover from ballistic to diffusive motion happened on a timescale too short to observe. While this rapid crossover simplifies the analysis of the motion, it poses a challenge to student understanding. This paper introduces a Brownian motion experiment in which a plastic disc is randomly driven by Faraday waves on a liquid surface. Video capture of the motion enables students to observe and analyze both the ballistic and the diffusive regimes. As a bonus, they will also be introduced to the fascinating phenomenon of Faraday waves. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:Brownian motion is the erratic motion of an object due to collisions with the fluid in which it is immersed. In this work, we detail a tabletop laboratory demonstration of underdamped Brownian motion wherein a macroscopic particle resting on a driven fluid interface exhibits ballistic motion at short times and diffusive motion at long times. We observe the trajectory of a centimeter-sized disk driven by a field of chaotic Faraday waves excited by a shaker. The crossover from ballistic to diffusive motion occurs at time and length scales experimentally accessible through particle tracking of a video recorded with a standard phone camera. Along with representative data, we provide a complete assembly guide and operating procedure for students so that the experiment can be readily applied in the classroom. The tabletop setup can also be adapted for other student projects and active research topics relating to particle motion on a vibrating fluid interface. Editor's Note: Normally when students observe Brownian motion in the lab, they have to accept that the crossover from ballistic to diffusive motion happened on a timescale too short to observe. While this rapid crossover simplifies the analysis of the motion, it poses a challenge to student understanding. This paper introduces a Brownian motion experiment in which a plastic disc is randomly driven by Faraday waves on a liquid surface. Video capture of the motion enables students to observe and analyze both the ballistic and the diffusive regimes. As a bonus, they will also be introduced to the fascinating phenomenon of Faraday waves. [ABSTRACT FROM AUTHOR]
ISSN:00029505
DOI:10.1119/5.0317318