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Anthony J. Creaco
Associate Professor
Department of Science
Borough of Manhattan Community College / City University of New York
Applying Newton’s Third Law of Motion in the Gravitron Ride 

A trip to an amusement park is the setting for this introduction to the concept of centripetal force in terms of Newton's laws of motion and vector quantities.  A student who is a physics major helps his friend understand the action-reaction forces that cause a body to stick to the wall of the Gravitron ride as it spins.  The case intentionally avoids the use of mathematics so that students will not get bogged down in solving equations while trying to internalize complicated concepts.  Instead, this introduction to the concept of centripetal force is intended as a jumping off point for more detailed discussions of the underlying mathematics. The case is appropriate for use in lower division undergraduate college or senior high school classes. It has been used with students in introductory physics classes for science majors and in non-majors general physics classes. It could also serve as the basis for an informal writing assignment in a writing intensive course.

Fooled by What We See: Looking into the Water and Snell’s Law

Most students have witnessed the refraction of light when viewing a partially submerged object—a spoon in a glass of water appears to bend—but they have little understanding of the phenomenon. The purpose of this case study is to elucidate the underlying principles and application of Snell's law to explain such illusions without the use of equations or numerical examples. It is intended to be an introduction to the topic and a starting point for the discussion of concepts related to the reflection and refraction of light through different media based on their indices of refraction. Using the familiar setting of a swimming pool, the case study relates fundamental principles of optics to observations that most students have personally experienced to explain these effects. This case study is appropriate for introductory physics classes at early college and senior high school classes. It can also serve as the basis for an informal writing assignment in writing intensive courses.