When Copper Wire Meets Al-Fed Liquid Metal: A Visual Demonstration of Self-Sustained Oscillation

Abstract Oscillation is a fundamental dynamic phenomenon in nature and technology. We present a visually striking and easy-to-implement demonstration experiment suitable for senior undergraduates in physics, chemistry, or materials science. When a copper wire is inserted into a droplet of aluminum-fed gallium–indium liquid metal (LM) immersed in aqueous NaOH solution, the wire begins to oscillate spontaneously and periodically. The motion is driven by a feedback loop between the aluminum–hydroxide reaction, localized hydrogen evolution, and asymmetric capillary forces at the three-phase contact line. The experiment uses only common materials (Ga–In alloy, aluminum foil, copper wire, NaOH), requires no complex instrumentation, and can be completed in less than 30 min. Its vivid, self-sustained oscillation engages students and illustrates core concepts of surface tension, reactive wetting, and chemically induced motion. Detailed safety precautions and waste-disposal protocols are provided, along with open-source video and motion-analysis files to facilitate adoption in the classroom. The demonstration also opens discussions on dynamic systems and the design of soft actuators.