Fig. 2.

Snapshots of the high-speed movie and the reconstructed images show particle positions in translating reference frames over time. Different initial conditions result in diverse type of dynamics: oscillation (A), slow converging (B), and passing (C). (A) In many cases, two particles undergo oscillatory movement before settling to a stable pair configuration. (B) Analogous to a critical damped oscillation, particles can settle to an ordered pair without oscillation. (C) Particles can pass each other when their z-position difference is large. (D) The second derivative of particle positions, from (A). Amplitude of peak acceleration decreases in consecutive interactions. Repulsive interaction peaks coincide with each other whereas attractive interaction peaks are asynchronous.