Motion of rain drops on a car side window

The present paper studies the initial motion of rain drops on a car side window. An explanation to the common observation of drops going up the window when a car reaches a given speed is provided, which takes into account the dimensions of the drops and the wind speed. We also discuss the importance of the actual window geometry, the state of the surface, and the drop size distribution. This work may thus be used as a basis for complete study of a population of drops against a car window.