This video shows some aspects of a "bubble" of non-contact formed in a chain sliding along a surface. The trajectories of material particles are compared with the corresponding ballistic trajectories which would occur if the particles were not attached to each other. The ballistic motions are initiated approximately at the points of greatest slope on the uptake side of the bubble. Significant deviation of the real trajectories from these ideal trajectories begins near the peak of the bubble.
Our primary interest is in the mechanics of the two points of discontinuity of contact that bookend the bubble. However, in the present video, we just want to show the beauty of the dynamics.
The chain (nickel-plated steel ball-and-link, 2 mm diameter balls with 3.5 mm center-to-center distance, Ball Chain Manufacturing, Mount Vernon, NY) is pulled at approximately 2.5 m/s along a wooden surface. We introduce the bubble using a retractable edge, seen on the lower right of the screen. We filmed at 2000 fps using a Photron UX100 camera and Nikon Nikkor 50mm f/1.4 lens, and employed the open source software suite PTVlab (Brevis et al. Experiments in Fluids 50:135-147 2011) and Matlab for particle tracking, and Mathematica for trajectory display.
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