URL: https://journals.aps.org/pre/abstract/10.1103/PhysRevE.107.034903
Abstract:
We present an experimental study of the dynamics of a set of
magnets within a fluid in which a remote torque applied by a
vertical oscillating magnetic field transfers angular momentum
to individual magnets. This system differs from previous
experimental studies of granular gas where the energy is
injected by vibrating the boundaries. Here, we do not observe
any cluster formation, orientational correlation and
equipartition of the energy. The magnets’ linear velocity
distributions are stretched exponentials, similar to
three-dimensional boundary-forced dry granular gas systems, but
the exponent does not depend on the number of magnets. The value
of the exponent of the stretched exponential distributions is
close to the value of 3/2 previously derived theoretically. Our
results also show that the conversion rate of angular momentum
into linear momentum during the collisions controls the dynamics
of this homogenously-forced granular gas. We report the
differences between this homogeneously-forced granular gas,
ideal gas, and nonequilibrium boundary-forced dissipative
granular gas.
Movie illustrating the motions of the magnets immersed in
water within the quasi-2D container.
The magnets' trajectories (red) are shown for 2 s (slow down 5
times).
The number of magnets is equal to N=20. The frequency and
amplitude of the magnetic field are 50 Hz and 162 G,
respectively.
The window size is equal to 11 x 6 cm2.