Adhesion is the phenomenon where two different surfaces or materials are held together by intermolecular forces, without the involvement of any intervening liquid. It is a fundamental concept that underpins various physical and biological processes, from the ability of geckos to climb walls to the cohesion of liquids and the function of biological membranes.
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Adhesion is responsible for the friction force between two surfaces in contact, which is essential for many mechanical systems and processes.
In the context of fluids, adhesion between the liquid and the surrounding solid surface is a key factor in determining the behavior of the fluid, such as its ability to rise up narrow tubes (capillary action) and the formation of droplets.
Adhesion between water molecules and the surfaces of biological membranes, such as cell walls, is crucial for the transport of nutrients, waste, and other substances across these barriers.
The adhesive properties of certain materials, such as the microscopic hairs on a gecko's feet, allow these animals to climb and adhere to vertical surfaces with ease.
Understanding and controlling adhesion is important in the design of various technologies, from the development of adhesives and coatings to the engineering of microfluidic devices and the study of biological systems.
Review Questions
Explain how adhesion is related to the concept of friction in the context of 5.1 Friction.
Adhesion is a fundamental aspect of friction, as it describes the intermolecular attractive forces that arise between two surfaces in contact. When two surfaces are pressed together, the adhesive forces between them contribute to the frictional force that opposes their relative motion. The strength of the adhesive forces depends on the materials involved, their surface roughness, and the area of contact, all of which influence the overall frictional behavior of the system.
Discuss the role of adhesion in the context of 11.1 What Is a Fluid?, specifically in relation to the behavior of liquids.
Adhesion plays a crucial role in the behavior of fluids, particularly liquids. The adhesive forces between the liquid molecules and the surrounding solid surfaces, such as the walls of a container, can lead to phenomena like capillary action, where the liquid is able to rise up narrow tubes against the force of gravity. This is due to the adhesive forces between the liquid and the solid surface overcoming the cohesive forces within the liquid itself. Adhesion also contributes to the formation of droplets and the wetting properties of liquids on different surfaces.
Analyze the relationship between adhesion, cohesion, and surface tension in the context of 11.8 Cohesion and Adhesion in Liquids: Surface Tension and Capillary Action.
Adhesion, cohesion, and surface tension are closely related concepts that govern the behavior of liquids. Cohesion, the intermolecular attractive forces between like molecules, gives liquids their unique properties, such as the ability to form droplets. Surface tension, the inward force acting on the surface of a liquid, is a result of these cohesive forces. Adhesion, the attractive forces between dissimilar molecules or surfaces, can counteract the cohesive forces and influence the behavior of liquids, such as their ability to rise up narrow tubes (capillary action) or spread out on different surfaces. The interplay between adhesion and cohesion is crucial in understanding the complex dynamics of liquids.
The inward force acting on the surface of a liquid, caused by the cohesive nature of the liquid molecules, which gives the surface a tendency to contract and behave like an elastic sheet.
The ability of a liquid to flow through narrow spaces or tubes without the assistance of, and in opposition to, external forces like gravity, due to the adhesive and cohesive forces between the liquid and the surrounding solid surface.