Synopsis: Dance of the Wedding Rings

Wedding rings spinning on a surface can follow surprising boomeranglike trajectories.
Synopsis figure
M. A. Jalali et al., Phys. Rev. E (2015)

A coin spinning on a flat surface spirals like a planet around a star until it falls on its side, rattles, and then abruptly stops. But Mir Abbas Jalali from the University of California, Berkeley, and colleagues have shown that twirling wedding rings follow a different dance. Shortly after a ring is set spinning, its path can take a sudden turn and the ring starts spiraling in the opposite direction, like a boomerang. The authors suggest this finding could be used to design objects that move over surfaces with complex reorientation capabilities.

Using high-speed imaging, Jalali and co-workers recorded the spinning motion of rings with different radii, widths, and thicknesses as they moved across various types of surfaces. They observed the same abrupt path turn in all of the experiments. Their numerical calculations suggest that this turn comes from a change in the ring’s air resistance shortly after it starts spinning.

When a coin spins, a thin layer of air gets trapped between its bottom edge and the surface on which it twirls. The same air layer appears when a ring is set spinning, but because of the big hole in the ring’s center the air can escape by flowing through the hole. This flow changes the frictional forces acting on the ring, causing a switch in its direction of motion. According to the authors, the ring can be likened to an object orbiting the Earth that is suddenly trapped by the moon’s gravitational field, becoming its satellite.

This research is published in Physical Review E

–Katherine Wright


Features

More Features »

Announcements

More Announcements »

Subject Areas

MechanicsInterdisciplinary Physics

Previous Synopsis

Particles and Fields

OPERA Bags Fifth Tau Neutrino

Read More »

Next Synopsis

Atomic and Molecular Physics

Gyroscopic Molecules

Read More »

Related Articles

Focus: <i>Video</i>—Slow-Motion Footage Captures Rubber Band Ripples
Mechanics

Focus: Video—Slow-Motion Footage Captures Rubber Band Ripples

Videos of a moving rubber band show that the band takes on previously unpredicted wavy shapes when it is shot through the air. Read More »

Synopsis: Extending the Kuramoto Model to Arbitrary Dimensions  
Complex Systems

Synopsis: Extending the Kuramoto Model to Arbitrary Dimensions  

The generalized version of a theory describing synchronization in an ensemble shows that coherence arises differently depending on whether the number of dimensions is even or odd.   Read More »

Synopsis: How Walkers Avoid Collisions
Interdisciplinary Physics

Synopsis: How Walkers Avoid Collisions

Observations of large numbers of pedestrians in two new studies offer insights into how humans avoid bumping into each other.   Read More »

More Articles