What is an example of a force of adhesion?

A prime example of a force of adhesion is the attraction between glue and paper.

Understanding Adhesive Forces

Adhesion refers to the attractive forces that occur between unlike molecules or surfaces. These intermolecular forces allow different substances to stick together, playing a vital role in both natural processes and numerous human-made applications. It is distinct from cohesion, which describes the attraction between like molecules.

Key Examples of Adhesion in Action

The concept of adhesion is best understood through practical illustrations, where substances bond due to these specific intermolecular attractions.

1. Glue and Paper

One of the most straightforward and common examples of adhesive forces is the attraction between glue and paper. When glue is applied, its molecules form strong attractive bonds with the molecules on the surface of the paper. This molecular interaction creates a secure connection, enabling the paper to firmly stick to another surface or to itself. This fundamental principle is why glues, tapes, and various bonding agents are so effective in holding materials together.

2. Water and Glass

Another excellent illustration of adhesion involves liquids, particularly water. Water is adhesive and tends to stick to the sides of a glass. This phenomenon is observable when you pour water into a glass; the water level often curves slightly upwards where it meets the glass surface. This curved surface is known as a meniscus.

Adhesion in water also contributes to more complex phenomena:

• Capillary Action: This occurs when the adhesive forces between water molecules and the inner surface of a narrow tube (like a plant's xylem or a thin glass tube) are stronger than the cohesive forces within the water itself. The strong adhesion pulls the water molecules up the sides of the tube, and cohesion then pulls the rest of the water column along, allowing water to rise against gravity.
• Concave Meniscus Formation: As mentioned, inside a test tube, the combined effect of water's adhesion and cohesion results in capillary action and the formation of a concave meniscus. The water molecules are more strongly attracted to the glass walls than to each other, causing the surface to dip in the middle and rise at the edges where it touches the glass.

Adhesive forces are fundamental to many everyday processes and advanced technologies, from the transport of water in plants to the manufacturing of composites and coatings. Understanding these forces helps explain why certain materials bond together and how liquids behave in various environments.