What's in a Name: Why Do We Call a Bouncy Ball Bouncy?

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© 2019 American Association of Physics Teachers. The ubiquitous bouncy ball, or "superball," is an engaging child's toy that has endured for more than 50 years. But what makes a bouncy ball so uniquely suited to its name? Steel balls, for example, are more highly elastic than are butadiene bouncy balls. Yet it is butadiene balls, and not steel balls, that appear in toy stores and vending machines across the globe. I present an experiment that uses the physics of inelastic collisions to provide compelling evidence for awarding butadiene balls the moniker "bouncy." In this experiment, students mimic the everyday use of bouncy balls by dropping steel and butadiene balls onto different surfaces from a modest range of heights. By analyzing videos of the bouncing balls, the students determine the coefficient of restitution and the energy loss - a key concept related to inelastic collisions - for each bounce of a ball. Having students capture videos using their own smartphone ensures that the students are comfortable with data taking and engaged in the activity. The data analysis uses simple yet powerful open-source video tracking software that further ensures that the experiment is accessible and low cost. The surprising results of this inquiry highlight the need to consider the material properties of both objects (ball and surface) when analyzing inelastic collisions. This important detail has been acknowledged yet not explicitly explored in other published experiments on the coefficient of restitution of bouncing balls.

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Physics Teacher

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