Adhesion Vs. Cohesion

• While cohesion is what keeps substances together, adhesion is what keeps substances stuck to different substances. This results from intermolecular forces, which can include hydrogen bonds and surface tension as well as partial electromagnetic charges on different parts of molecules. All substances display a certain degree of adhesion and cohesion, though the types of material they tend to adhere to is different from substance to substance.
  
  

Wettability

• Wettability is the ability of a surface or substance to get wet. Because water is a polar molecule and has partial charges on different areas of the individual molecules, it will wet surfaces that also have partial charges. However, substances that do not have polar molecules will not get wet with water. This is why water beads up on wax or other oil-based substances. The ability of a surface to get wet allows basic biological functions to take place.
  
  

Lubrication

• Both adhesion and cohesion is essential in the process of lubrication, which uses a substance medium to keep objects from rubbing together. Adhesion is important in lubrication because it keeps the lubricant stuck to the material. Cohesion is important because the lubricant will hold together and keep the materials from rubbing together. A practical example of lubrication is the use of motor oil in a car. The oil sticks to the motor's moving parts, which keeps them running smoothly and prevents them from grinding together.
  
  

Glues and Adhesives

• An obvious use of adhesion is in adhesives and glues. Without adhesion, there would be no way to hold two objects together without physically connecting them. Glue, paste and other sticky substances adhere to objects and literally keep things from falling apart.
  
  

Biological Implications

• Adhesion is essential to many biological functions. Bones in joints have a special coating that keeps them from rubbing together. Tendons and ligaments firmly hold bones and muscles together. Even processes at the cellular level require adhesion, including the formation of cells, the production of proteins and the replication of genetic material.