An Inventory on the Principle of Relativity and the Principle of Equivalence in Classical Mechanics: Investigating Misconceptions and Reasoning Pitfalls

Abstract

Identifying and addressing students’ conceptual difficulties are central goals of physics education research. This study examines the understanding of fundamental concepts of classical relativity - including the Frame of Reference, the Principle of Relativity and the Principle of Equivalence - by university students. We developed the Classical Relativity Concept Inventory (CRCI), a 21-item multiple-choice test, designed to diagnose misconceptions and reasoning difficulties in these domains. The CRCI was administered to a sample of 267 first-year Physics students following formal instruction on relative motion. Comprehensive statistical analyses, including Classical Test Theory, Rasch modeling, Factor Analysis and Cluster Analysis, were conducted to evaluate the test’s psychometric properties and diagnostic effectiveness. Results indicate that the CRCI is a reliable and discriminating instrument; specifically the Factor Analysis confirmed a multi-dimensional structure while Cluster Analysis revealed four distinct conceptual components and identified four student profiles exhibiting varying degrees of mastery, clearly demonstrating a persistent struggle in conceptualisation and reasoning about relative motions and non-inertial systems. These findings provide actionable insights for improving instruction on classical relativity, emphasizing the need to explicitly address common conceptual pitfalls.