A dual-flywheel spinning top

The precessional motion of a spinning top can be analysed, described, and interpreted at various levels of detail ranging from phenomenological and semi-qualitative to fully quantitative descriptions, depending on the students’ prior knowledge, ranging from primary school up to the early years of physics degree programs (and beyond, owing to its quantum counterparts). This phenomenon offers an opportunity to foster scientific observation of phenomena that appear simple, yet are non-trivial and in some respects counterintuitive, as well as to introduce or deepen understanding of concepts with significant educational value. We propose a system that has several aspects in common with conventional spinning tops but allows for additional experimental checks, enabling a more in-depth exploration of some important details and eliminating potential sources of misunderstanding. The system consists of a pair of independent flywheels mounted on a frame that can be made to precess. Among the observations that can be made, we consider demonstrating the vector nature of angular momentum and the distinct roles of internal and external torques acting on a system. We provide some construction details for building such a system using readily available low-cost materials, possibly requiring access to basic workshop tools and/or a 3D printer.