Abstract: Taking the friction between the wooden block and the wooden desktop and the car tires and the ground as an example, the mechanism of the influence of the amount of water on the friction between the objects is analyzed. Analysis shows that the surface energy of water between the grooves in the wooden block will produce additional friction, the additional force and its corresponding friction force increase and then decrease with the increase in water volume; car driving in the presence of water film on the road surface, the impact of the water film reduces the pressure of the tires on the ground, thus reducing friction, the thicker the water film, the faster the driving speed, the smaller the friction between the tires and the ground.

Key words:  friction, surface energy, mechanism