Water Bending

It is well-known that a thin stream of water (droplets) bends near an electric charge. However, anecdotal evidence suggests that the physical reason behind this water bending is less well-known. There are (at least) three possible models: the large dipole moment of the water molecule, ions dissolved in the water, and triboelectric charging. A handful of simple experiments can be designed to distinguish between these models unequivocally. The experiments can be performed using standard undergraduate electrostatic lab equipment. The analysis of the experiments is primarily conceptual and does not require anything beyond basic algebra. Thus, the water-bending problem provides an ideal situation for training students in the scientific method. Therefore, I propose that the water bending problem can be used, very effectively, as a simple, but challenging, inquiry-based lab to train students (and perhaps even instructors) in designing, performing, and evaluating experiments to distinguish between models.