Speaker
Description
Beach balls from 4-inch to 24-inch diameter were dropped from a 5-meter high balcony to demonstrate the important effects of buoyancy, drag and spin (Magnus) forces on slow moving beach balls. These activities were part of a class taken by students during summer session. The large size to mass ratio of the beach ball allows drag and Magnus effects to be easily observed at speeds and times convenient to make simple measurements. Measurements were made by dropping beach balls with and without spin from the 5-m high balcony overlooking a large entrance hall and study area. Videos at 60 Hz frame rate of the dropped beach balls together with giant wide paper rulers taped along walls and a large digital clock were recorded with an iPhone. Frame by frame video playback allowed determination of distance, velocity and spin rates from which drag and lift coefficients were determined using simplifying assumptions. A discussion of this analysis and comparison with other results will be given.
