The Force of Cohesion and The Force of Adhesion

The Force of Cohesion.

The force of  attraction between the molecules of the same substance  is called cohesion. In case of solids, the force of cohesion is very large and due to this solids have definite shape and size. On the other hand, the force of cohesion in case of liquids is weaker than that of solids. Hence liquids do not have definite shape but have definite volume. The force of cohesion is negligible in case of gases. Because of this fact, gases have neither fixed shape nor volume.

Examples :

i) Two drops of a liquid coalesce into one when brought in mutual contact because of the cohesive force.

ii) It is difficult to separate two sticky plates of glass wetted with water because a large force has to be applied against the cohesive force between the molecules of water.

iii) It is very difficult to break a drop of mercury into small droplets because of large cohesive force between mercury molecules.

 Force of Adhesion.

The force of attraction between molecules of different substances is called adhesion.


i) Adhesive force enables us to write on the black board with a chalk.

ii) Adhesive force helps us to write on the paper with ink.

iii) Large force of adhesion between cement and bricks helps us in construction work.

iv) Due to force of adhesive, water wets the glass plate.

v) Fevicol and Gum are used in guing two surfaces together because of adhesive force.

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