What are Molecular Forces?

Molecular attraction is a force which acts in such a way as to bring all the particles of a body together. It acts in threep. 83 ways, dependent on the particular conditions which exist.

First: Cohesion

This exists between molecules which are of the same kind, as for instance, iron. Cohesion of the particles is very strong in solids, much weaker in liquids, and scarcely exists at all between the particles in gases.

Second: Adhesion

Adhesion is that property which exists between the surfaces of bodies in contact. If two flat surfaces are pressed together, as for instance, two perfectly smooth and flat pieces of lead, they will adhere. If, for instance, oil should be put on the surfaces, before putting them together, they would adhere so firmly that it would be difficult to pull them apart.

Third: Affinity.

This is another peculiarity about materials. Thus, while cohesion binds together the molecules of water, it is chemical affinity which unites two elements, like hydrogen and oxygen, of which water is composed.

Excerpt from:
Title: Practical Mechanics for Boys
Author: J. S. Zerbe

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