Abstract
Steady dissipation of energy is a crucial property that distinguishes active particles from Brownian particles. However, it is not straightforward to explicitly model the dissipative property of existing active particles driven by a vibrating plate. We present a novel active particle that can be explicitly modeled by Newtonian dynamics of a conservative force field plus two asymmetrical dissipative terms. The particle is a dimer consisting of two ping-pong balls connected by a rigid rod, and its two balls are filled with granular particles of the same total mass but of different grain size. This dimer placed on a vibrating plate exhibits 3 types of motion – by tuning the frequency and the amplitude of the vibration, the dimer undergoes either a directed motion toward the small (or large) grain-filled side or an unbiased random motion. We investigate the various modes of motion both experimentally and numerically and show that the directed motion is a result of the asymmetric damping due to the size difference in the filling grains. Furthermore, the numerical simulation reveals that the dimer’s dynamics in either directed motion mode resembles a limit cycle attractor that is independent of its initial condition.
Highlights
The broken time reversal symmetry by the dissipation of energy distinguishes active matter from a system of Brownian motion1
We report a novel design of a tunable active dimer – two grain-filled ping-pong balls firmly connected by a rigid rod – that is able to perform horizontal self-propulsion on a plate under vertical vibration
One mode is denoted as the toward-large-grain mode (TLG), where the net motion of the dimer is biased towards the ball filled with large grains (LG ball)
Summary
The broken time reversal symmetry by the dissipation of energy distinguishes active matter from a system of Brownian motion. The dimer is able to respond to the plate’s vibration with various distinctive modes of self-propelled motion This design is inspired by the earlier studies of a grain-filled bouncing ball on a vibrating or a static plate[19,20,21], in which the coefficient of restitution and its resulting bouncing dynamics demonstrate rich dependence on the mass and size of grains inside the bouncing ball. A conservative force field, a combination of a symmetric and an asymmetric damping term that dissipate energy and break the symmetry of the dynamics In this manuscript, we mainly focus on two prominent types of self-propelled motion completely opposite directions by tuning the vertical vibration of the plate. Readers are referred to Supplementary Information for more details of both experimental and numerical methods involved in this study
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