Adhesion and Cohesion

Matter is made up of molecules. That exerts force of attraction. This force of attraction may be either Cohesion or Adhesion.

 Cohesion is the force of attraction between the molecules of the same substance, example water to water molecules.

 Adhesion is the force of attraction between the molecule of different substances example water to glass molecules.


Water molecules can experience the force of cohesion among themselves, where water molecules and glass molecules will experience force of adhesion.
Definite shapes of a solid are due to strong cohesion force among its molecules.


Shapes and meniscus of a liquid

When we carried out activities involving determination of volume in a liquid ring and measuring cylinder. The description indicated that the surface of the liquid was carved, forming a meniscus, and that the volume must be read at the bottom or top of the meniscus, depending on the liquid used. For mercury, the top of the meniscus is read.

The formation of a meniscus in a liquid is due to forces of adhesion between the liquid and the walls of the container. The adhesion of the liquid such as water to the wall of a vessel causes an upward force on the liquid at the edge.

The opposite takes place in mercury, the meniscus of water curves upwards forming a concave shape. When a drop of each liquid, mercury and water are placed on a glass sheet, water spreads further unlike mercury, because of mercury's high cohesion force among its particle.

  • Why water wets the glass?
  • Why methanol does not wet the glass?

Applications of Adhesion and Cohesion in Daily Life

1. To stick two different objects together. Here we use the adhesive effects of tape or glue.

2. Adhesion can also be used to remove harmful materials such as bacteria from drinking water. Adhesive forces are the source attraction substance.

3. Cohesion assists in transport of water in plants and animals by allowing one molecule to pull others along with it.

4. The bodies of plants and animals also use the cohesion of tissue to repair damage.

5. Ink sticks on paper because of adhesive force between the paper and ink.


Surface Tension

While you may not be able to walk on water, water stride does. This is due to the property of liquid, which is known as surface tension.

Surface tension is the ability of the molecules on the surface of a liquid to attract and stick to each other allowing them to resist an external force. Surface tension enables insects such as water strides and mosquitoes to walk on water. It allows small objects even metallic ones such as needles and razor blades to float on the surface of water.



Surface tension is a resultant attractive force between molecules in a liquid. The molecules below the surface liquid have forces of attraction between neighbouring particles. However molecules at the surface have no neighbouring molecules above them. This makes them have stronger attractive force than their nearest neighbours on the surface.

However, when some detergent is added to water, the same objects sink to the bottom of the trough. This means that the detergent interfered with the surface of the liquid so decreasing the tension of the water surface.

Detergents are example of surfactants. A surfactant is a substance that reduces the surface tension of a liquid.


Note: the term surfactant is an aerogun for surface-active agent.
Surface tension is affected by the following
 Nature of the liquid
 Contamination/impurities
 Temperature


Application at surface tension:

1. In extraction of impurities dating laboratory process.

2. Surfactants are also used to make emulsion of liquid like oil and water.

3. In cleaning action of soap.


Applications of Surface Tension in Daily Life

1. In extraction of impurities dating laboratory process

2. Surfactants are also used to make emulsion of liquid like oil and water.

3. In cleaning action of soap