Introduction

What this section sets up

Of the three states of matter, a solid nearly keeps its own shape and volume even under a large force, while liquids and gases take the shape of the containing vessel and flow under an external force. A fluid means a substance that can flow, so liquids and gases together are called fluids: a fluid either has no rigidity or has very low rigidity.

The chapter deals with the mechanical properties of liquids and gases only — the pressure a fluid exerts at rest and in motion, viscosity, and surface tension. There is no separately examinable result in this section; it is orientation for the sections that follow.