why do beads of water form on a slippery surface,such as a freshly waxed car?
Water does not have a strong attraction to wax, so the surface tension of the water causes it to form a spherical skin around water droplets.
When beads of water form on a slippery surface, such as a freshly waxed car, it is due to a phenomenon called surface tension. The surface tension is caused by the cohesive forces between the water molecules.
To understand why water forms beads on a slippery surface, you need to consider two main factors: adhesion and cohesion. Adhesion refers to the attraction between water molecules and other surfaces, while cohesion refers to the attraction between water molecules themselves.
On a freshly waxed car, the wax forms a hydrophobic (water-repellent) surface. When water comes into contact with the wax, it does not easily spread out. Instead, it tends to form droplets or beads due to the high cohesion of water molecules. The cohesive forces between the water molecules are much stronger than the adhesive forces between water and the wax surface.
Additionally, the surface tension of water plays a significant role. Surface tension is a property of liquids that allows them to resist external forces and minimize their surface area. It is caused by the imbalance of forces between the molecules on the surface and those in the interior.
The water molecules at the surface experience a net inward force, which causes the surface to behave like a stretched elastic membrane. This surface tension forces the water droplets to form spherical shapes, as it minimizes the surface area and creates the smallest possible shape.
Therefore, on a freshly waxed car or any other slippery surface, the water molecules tend to form beads due to the combination of hydrophobic properties and high cohesion. The surface tension of water further promotes the formation of compact spherical droplets.
In summary, the beads of water form on slippery surfaces because the water molecules prefer to stick together (cohesion) rather than spreading out on the surface (adhesion). The wax or other hydrophobic materials contribute to the water's inability to spread, while the surface tension of water helps to shape it into droplets.