Student project: Of spinning coins and merging black holes

TL;DR

This paper presents a simple, educational experiment using a spinning coin to illustrate principles of gravitational wave phenomena and energy dissipation, inspired by LIGO's detection of black hole mergers.

Contribution

It introduces a tabletop demonstration of transient phenomena involving frequency and amplitude modulation, linking classical physics with gravitational wave concepts.

Findings

Coin spin demonstrates energy dissipation via sound and heat.

Vacuum chamber use isolates air viscosity effects.

Educational tool for physics principles related to gravitational waves.

Abstract

For the past decade, the SAIL labs at the University of Sydney have been challenging students with short research projects that elucidate basic principles of physics. These include the development of instruments launched on cubesats, balloons, on telescopes or placed out in the field. This experiment is inspired by the spectacular 2015 discovery of merging black holes with the Laser Interferometric Gravitational-Wave Observatory (LIGO). Students are profoundly inspired by LIGO, and for good reason, but it is challenging to construct a table top demonstration of a gravitational wave observatory. Instead we consider chirps which are remarkable transient phenomena in nature involving both frequency and amplitude modulation, as we can demonstrate with a spinning coin. In the case of the LIGO event, orbital energy is being released as gravitational radiation; for the spinning coin, its spin/orbit energy is being released dissipatively (sound, heat, air viscosity). Our experiment involves a simple device to spin a coin remotely. This aids repeatability and allows us to spin the coin within a vacuum chamber to examine the contribution of air viscosity.