Illustration of buoyancy and drag force

• C+30+110

This is an illustration of the interaction of buoyant and drag force. To remind students of the effect of drag force a ball can be dropped in air and then dropped in water or glycerin to show a dramatic change in falling velocity. The main demo is four marbles of different radii which are stored in four different glycerin containers. These marbles are less dense than glycerin so they rise in the tubes. A student may assume that the larger ball will rise more slowly than a smaller ball due to the drag force however performing the demo illustrates that this is not the case. This demonstration may be more effective if a think-pair-share question or similar instrument is used to probe student conceptions about the results prior to demonstration.