Water Drop Race
Watch a drop of water on a slide
By releasing a water drop on the toboggans you start a race. You can observe how they ride on the slide and tip which drop will win. All toboggans look the same and all drops are the same size. What is different is the toboggan??™s surface. Have you ever tried to dip a wax candle in water or write with a felt-tip pen on a plastic surface? Some liquids and surfaces simply don??™t match. In the case of water these surfaces are termed hydrophobic. The drop hardly touches such a surface and forms little balls which roll easily. The more the water drop touches the surface, the more it sticks to it and when it is to move there is greater friction and sliding is more difficult. This type of surface is called hydrophilic.
