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Cohesion and adhesion
Beginner
Attraction between like and unlike molecules.
Cohesion is attraction between like molecules (surface tension), adhesion between unlike (wetting). Their balance determines the contact angle.
Water sticks to glass; mercury sticks to itself.
Both are electromagnetic in origin.
In more detail
Cohesion is the attraction between like molecules, and adhesion is the attraction between different molecules, such as liquid and solid. Their balance determines wetting, capillary rise and surface shape.
Real-world uses
- Glues rely on strong adhesion between adhesive and the surfaces.
- Water drops cling to glass because adhesion is stronger than cohesion.
- Water beads on a waxed car but spreads on a clean windscreen, showing the balance of cohesion and adhesion.
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Frequently asked questions
What is the difference between cohesion and adhesion?
Cohesion is attraction between the same substance, and adhesion is attraction between different substances.
Why does water stick to glass?
Because water molecules attract glass more strongly than they attract each other.
What is the difference between cohesion and adhesion?
Cohesion is the attraction between like molecules, while adhesion is the attraction between a liquid and a different material.
Related topics in Fluids & Elasticity
Excess pressure in drops and bubbles · Angle of contact · Capillary rise · Elasticity · Stress · Strain