In chemistry, adhesion refers to the tendency of unlike molecules to bond with one another, while cohesion refers to the attractive force between molecules of the same type. Surface tension, which is an essential property of water, illustrates the relationship between adhesion and cohesion.
The forces of adhesion can be the result of mechanical or electrostatic forces exerted on two different substances. Meanwhile, cohesive forces are generally associated with hydrogen bonding and Van der Waals forces, which cause liquids, particularly water, to withstand separation. When water is poured over a glass surface, both adhesive and cohesive forces act on the water. A stronger adhesive force tends to spread the liquid over the surface, while a stronger cohesive force tends to form water droplets on the surface.