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Water molecules have an amazing ability to stick to each other. This happens because of a unique attraction known as cohesive forces. The primary driver of these forces in water is hydrogen bonding.
Hydrogen bonds occur when the positive end of one water molecule gets attracted to the negative end of another. The result? Water molecules cling tightly to each other, almost like a tiny magnet. When water beads up, it shows how strong these cohesive forces are. The water molecules prefer to pull together, resisting any external pressure to spread out. This trait aids in creating a rounded and compact shape, like a bead, as the water pulls inward.
You'll notice this effect prominently on surfaces where water does not want to spread or stick.

Have you ever wondered why some surfaces repel water so effectively? Well, this is due to hydrophobic properties. The term "hydrophobic" means "afraid of water". Surfaces with these properties, like wax, repel water rather than allowing it to spread out. Wax on a car acts as a hydrophobic shield. Since wax does not mingle well with water, the water doesn't want to spread into a thin layer. It clings to itself in a beaded form because of the underlying repulsion from the wax. This behavior is crucial for understanding why water simply rolls off a well-waxed car.
Think of this like oil on water; they just don't mix, showcasing similar repellence.

Ever noticed how insects can walk on water without sinking? That's because of a phenomenon called surface tension. In water, this tension arises due to the cohesive forces between molecules.
Surface tension is essentially the "skin" on the water surface that tries to make the water occupy the least possible surface area. Due to high surface tension, water droplets form beads, minimizing contact with surfaces they rest upon. It's like the water droplet is forming a tiny dome, holding itself up.
On a waxed car, the tension remains high as the water doesn’t interact much with the wax, letting droplets maintain their shape smoothly.

Adhesion is like a sticky handshake between two different substances. It’s the attraction between water molecules and another surface.
The magical part is, when adhesion forces are stronger than cohesive forces, water spreads out instead of forming beads. Imagine a car that's dirty and unwaxed. Here, water molecules easily find things to cling onto in the dirt, creating a strong adhesive bond. This results in water spreading out, covering more of the surface, unlike on a waxed car.
Adhesion tells us why on some surfaces like paper towels, water spreads quickly as the attraction between molecules is quite strong.