Adhesion

Definition

Adhesion is the intermolecular force that causes two surfaces or materials to cling together. It is a fundamental concept in the study of friction, as adhesion contributes to the frictional force between surfaces in contact.

5 Must Know Facts For Your Next Test

1. Adhesion is the primary cause of friction between two solid surfaces in contact, as the surfaces cling together due to intermolecular attractive forces.
2. The strength of adhesion depends on the materials involved, the surface roughness, and the presence of any intervening substances, such as lubricants or contaminants.
3. Adhesion can be increased by roughening the surfaces, as this increases the surface area and the number of molecular interactions between the materials.
4. Capillary action, the ability of a liquid to flow into narrow spaces without the assistance of, or even in opposition to, external forces, is a result of adhesion between the liquid and the surrounding solid surfaces.
5. Understanding adhesion is crucial in the design of mechanical systems, as it affects the performance and efficiency of moving parts, such as bearings and gears.

Review Questions

• Explain how adhesion contributes to the frictional force between two surfaces in contact.
  • Adhesion is a primary contributor to the frictional force between two surfaces in contact. When two surfaces are pressed together, the intermolecular attractive forces between the atoms or molecules on the surfaces cause them to cling to each other, creating a resistance to relative motion. This adhesive force must be overcome to initiate or maintain sliding motion between the surfaces, resulting in the frictional force. The strength of the adhesion depends on the materials involved, the surface roughness, and the presence of any intervening substances, all of which can affect the magnitude of the frictional force.
• Describe how the concept of adhesion is related to the phenomenon of capillary action.
  • Adhesion is the underlying mechanism that enables capillary action, the ability of a liquid to flow into narrow spaces without the assistance of, or even in opposition to, external forces. When a liquid comes into contact with a solid surface, the adhesive forces between the liquid molecules and the solid surface can cause the liquid to be drawn into small spaces or tubes, even against the force of gravity. This happens because the adhesive forces between the liquid and the solid surface are stronger than the cohesive forces between the liquid molecules, allowing the liquid to 'climb' the solid surface. Understanding adhesion is crucial in explaining and predicting the behavior of liquids in narrow spaces, which has important applications in various fields, such as fluid mechanics and material science.
• Analyze how the concept of adhesion can be applied to the design and optimization of mechanical systems, such as bearings and gears.
  • The concept of adhesion is essential in the design and optimization of mechanical systems, as it affects the performance and efficiency of moving parts. In the case of bearings, the adhesive forces between the bearing surfaces and the shaft or housing can contribute to the frictional forces, leading to energy losses and wear. By understanding and controlling the adhesion between these surfaces, engineers can design bearings with reduced friction and improved longevity. Similarly, in gears, the adhesion between the gear teeth can influence the transmission of power and the wear of the gear surfaces. Careful consideration of the materials, surface roughness, and any lubricants used can help minimize adhesion-related issues and optimize the performance of mechanical systems. Additionally, the concept of adhesion is crucial in the development of advanced materials, coatings, and surface treatments that can reduce friction and wear in various engineering applications.

Related terms

Cohesion: The intermolecular attractive force that holds together the molecules within the same material or substance.

Surface Tension: The inward force acting on the surface of a liquid, caused by the cohesive forces between the liquid molecules.

Wetting: The ability of a liquid to spread on and adhere to a solid surface, determined by the balance of adhesive and cohesive forces.