Why does water bead up better on a well waxed car?
Water is a polar molecule, composed of two hydrogen atoms bonded to a single oxygen atom. Water molecules like to stick to one another, like small magnets. This is called cohesion. Water molecules also can be attracted to other substances, such as metal or dirt, especially if they have some static charge on them. This is called adhesion. Lastly, some substances are not at all attracted to water, and even repel it. These include oils, fats and waxes; all of which are called non-polar substances. When water falls on an unwaxed car, the forces of adhesion are almost as strong as the forces of cohesion, and the water spreads out. Furthermore, if the painted surface is not perfectly smooth, water can be channeled for some distance along tiny ridges and valleys. This is particularly true if there is dirt on the car. The dirt itself may be charged, and attract water even more. These tiny flaws may not be readily visible without a magnifying glass, but you can sense a rough surface when you ru
