The particles of matter in solids and liquids are held together by a force called cohesion. This cohesive force is stronger in some bodies than in others. Sometimes the word tenacity is used instead of cohesion. We may speak of a substance as possessing great tenacity or great cohesion; such a substance is said to be tenacious. Correctly speaking, tenacity is the measure of cohesion.

The property of a substance which enables it to stick or cling to another substance is called adhesion. Glue, for instance, is held to wood by adhesion.

Inertia is the tendency of a body to retain its condition of rest or of motion. The inertia of a hammer prevents it from moving itself. A lathe tends to run after the power is shut off.