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Adhesive and Cohesive Forces

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Last updated date: 24th Feb 2024
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What are Adhesive and Cohesive Forces?

Cohesive and adhesive forces are fundamental concepts in physics and chemistry that govern the behavior of substances. Cohesive forces refer to the attraction between molecules of the same substance, while adhesive forces are the attraction between molecules of different substances. A common real-life example is the way tea forms a rounded shape at the brim of a cup due to cohesive forces within the liquid and adhesive forces between the tea and the cup's inner surface. Understanding these forces helps explain phenomena like surface tension and material adhesion.


Adhesive Force:

Adhesive forces are the attractive forces between molecules of different substances. These forces enable the molecules of one substance to adhere or stick to the molecules of another substance. Adhesive forces are responsible for phenomena like capillary action, where liquids rise or fall in narrow tubes against the force of gravity.


An example of adhesive forces can be seen when water adheres to the walls of a glass tube. The adhesive forces between the water molecules and the glass surface allow the water to climb the walls, defying gravity, and creating the meniscus (curved surface) observed in graduated cylinders.


Cohesive Force:

Cohesive forces refer to the attractive forces between molecules of the same substance. These forces hold the molecules together and give rise to the cohesive properties of the material. The strength of cohesive forces determines the physical state of matter, such as whether a substance exists as a solid, liquid, or gas.


Examples of cohesive forces can be observed in liquid water. The hydrogen bonds between water molecules create a strong cohesive force, allowing water to form droplets and exhibit surface tension. The high surface tension of water allows some insects, like water striders, to walk on its surface without sinking.


Comparison between Adhesive and Cohesive Forces:

Understanding the distinction between adhesive and cohesive forces is important in various scientific fields, as they have significant implications for phenomena such as adhesion, surface tension, and material behavior.


The table describes the comparison between adhesive and cohesive forces:


Adhesive Force

Cohesive Force

Adhesive force is an attractive force between molecules of different substances.

Cohesive force is an attractive force between molecules of the same substance.

Adhesive forces occur between molecules of different substances, allowing them to stick or adhere to each other.

Cohesive forces occur between molecules of the same substance, this force binds the same molecules.

Adhesive forces are responsible for adhesion and bonding between different materials.

Cohesive forces determine the cohesive properties of a substance, such as its ability to maintain its form and flow.

Adhesive forces contribute to the shape of the meniscus, which is the curved surface of a liquid in a container.

Cohesive forces also influence the meniscus, as they determine the curvature and behavior of the liquid's surface.

Adhesive forces can be observed when water adheres to the walls of a glass container, or when glue sticks two surfaces together.

An example of cohesive forces is observed in liquid water, where hydrogen bonds between water molecules create a strong cohesive force, allowing water to form droplets and exhibit surface tension.


Reactions of Adhesive and Cohesive Forces

What is adhesive and cohesive force reactions? This plays a significant role in various natural and man-made processes. These reactions arise from the intermolecular forces between molecules and are responsible for a range of phenomena, including the adhesion of materials, the formation of droplets, and the behavior of liquids and solids. There are various adhesive and cohesive force reactions examples which will be discussed in further.


Let's explore the reactions of adhesive and cohesive forces:


Adhesive Force Reaction:

Adhesive force reactions occur when molecules from one substance interact with molecules from another substance and form strong bonds. Examples of adhesive force reactions can be seen in everyday situations. When using glue to stick two surfaces together, the adhesive forces between the glue and the surfaces allow them to adhere firmly. Similarly, adhesive forces enable the tape to stick to paper or walls, creating a temporary bond. Adhesive force reactions are also at work when water adheres to the walls of glass, creating a meniscus.


The strength of adhesive forces determines the effectiveness of adhesion between materials. If the adhesive forces are strong, the materials will have a firm and durable bond. Conversely, if the adhesive forces are weak, the bond between materials may be less secure.


Cohesive Force Reaction:

Cohesive forces unite molecules of the same substance, forming an invisible bond that holds them together and defines the cohesive properties of the material. Cohesive force reactions occur when molecules within a substance interact with one another, forming stable arrangements.


One of the most common examples of cohesive force reactions can be found in liquid water. The hydrogen bonds between water molecules create a strong cohesive force that keeps the molecules tightly connected. This cohesion allows water to form droplets, exhibit surface tension, and maintain its liquid state.


Cohesive force reactions are responsible for the behavior of liquids and solids. For example, the cohesion between particles in a solid material gives it its strength and integrity. In the case of liquid substances, cohesive forces contribute to properties such as viscosity and the ability to maintain a specific shape.


Conclusion:

Adhesive and cohesive forces are important concepts that describe how different substances stick together and how molecules within a substance stay united. Adhesive forces are like glue that helps materials bond together, such as when we use glue or tape. On the other hand, cohesive forces are the forces that hold molecules of the same substance together, giving the material its unique properties. Understanding these forces is valuable for fields like biology and engineering, as they affect things like how cells stick together or how liquids behave. By studying adhesive and cohesive forces, scientists can make advancements in areas like materials and technology.

FAQs on Adhesive and Cohesive Forces

1. How do cohesive and adhesive forces affect surface tension?

Cohesive forces contribute to the high surface tension of liquids, such as water, while adhesive forces enable liquids to adhere to solid surfaces, altering the shape and behavior of the liquid at the interface.

2. Can you provide another example of cohesive forces?

One example is that the cohesive forces between the carbon atoms in a diamond, which give the material its hardness and solid structure.

3. How are cohesive and adhesive forces relevant in everyday life?

Adhesive forces bond materials in manufacturing, carpentry, and electronics. Cohesive forces aid nutrient transport in plants and enable swallowing. Adhesive forces help paint adhere and bandages stick, while cohesive forces aid transdermal medication delivery.