What is an adhesive?

An adhesive is defined as a substance that holds materials together by surface attachment. This definition highlights the primary function of adhesives, which is to create a bond between surfaces at the molecular level. When applied, an adhesive penetrates the surfaces of the materials and forms stronger chemical or physical bonds once it cures or sets. This can happen through various mechanisms, including chemical reactions, moisture evaporation, or pressure.

Adhesives can bond a wide variety of materials, including metals, plastics, wood, and ceramics, making them versatile in applications ranging from construction to manufacturing and arts and crafts. Their application is essential in many engineering practices where traditional fasteners, like screws or nails, may not be suitable due to aesthetics or the need for a more uniform distribution of stress.

The other options refer to concepts that don't accurately represent what an adhesive is. For instance, a chemical compound that does not bond materials does not serve the purpose of an adhesive, while a mechanical fastener typically relies on physical interlocking rather than surface attachment. Lastly, defining adhesive solely as a type of glue limits the understanding of the broader category of adhesives, which can include various materials with different properties and uses beyond traditional glue.