Distinguishing energy conservation from mechanical energy conservation using a bouncing ball: undergraduate laboratory experiment

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Abstract
This paper presents a laboratory experiment designed to help undergraduate engineering students distinguish between the general principle of energy conservation and the conditional conservation of mechanical energy. Using the accessible system of a vertically bouncing ball, the experiment employs temporal measurements of successive rebound intervals. From these measurements, students determine the coefficient of restitution and quantify mechanical-energy loss during impacts without relying on fitting procedures or image analysis. The experiment is configured to minimize the influence of air resistance through the choice of small, relatively dense balls and modest release heights, ensuring that energy dissipation is dominated by non-conservative processes during the collision. The activity was implemented on a large scale with approximately 400 first‐year students across two study programs. Student results exhibit a high degree of reproducibility, with clear distinctions between rigid and soft impact surfaces. The experiment proved robust, conceptually transparent, and well aligned with the learning objective of clarifying the limitations of mechanical‐energy conservation. Its simplicity, scalability, and strong diagnostic value make it a valuable addition to introductory physics laboratory curricula.

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