Cited Passage

CHAPTER 2 — Underwater Physics 2-1 CHAPTER 2 Underwater Physics 2-1 INTRODUCTION 2-1.1 Purpose. This chapter describes the laws of physics as they affect humans in the water. 2-1.2 Scope. A thorough understanding of the principles outlined in this chapter is essential to safe and effective diving performance. 2-2 PHYSICS Humans readily function within the narrow atmospheric envelope present at the earth’s surface and are seldom concerned with survival requirements. Outside the boundaries of the envelope, the environment is hostile and our existence depends on our ability to counteract threatening forces. To function safely, divers must understand the characteristics of the subsea environment and the techniques that can be used to modify its effects. To accomplish this, a diver must have a basic knowledge of physics—the science of matter and energy. Of particular importance to a diver are the behavior of gases, the principles of buoyancy, and the properties of heat, light, and sound. 2-3 MATTER Matter is anything that occupies space and has mass, and is the building block of the physical world. Energy is required to cause matter to change course or speed. The diver, the diver’s air supply, everything that supports him or her, and the surrounding environment is composed of matter. 2-3.1 Elements. An element is the simplest form of matter that exhibits distinct physical and chem ical properties. An element cannot be broken down by chemical means into other, more basic forms. Scientists have identified more than 100 elements in the phys ical universe. Elements combine to form the more than four million substances known to man. 2-3.2 Atoms. The atom is the smallest particle of matter that carries the specific properties of an element. Atoms are made up of electrically charged particles known as protons, neutrons, and electrons. Protons have a positive charge, neutrons have a neutral charge, and electrons have a negative charge. 2-3.3 Molecules. Molecules are formed when atoms group together ( Figure 2-1 ). Molecules usually exhibit properties different from any of the contributing atoms. For example, when two hydrogen atoms combine with one oxygen atom, a new substance—water—is formed. Some molecules are active and try to combine with many of the other molecules that surround them. Other molecules are inert and

The PDF viewer opens on the cited page and searches this passage for highlight.