LEARNING GOALS In this chapter, you will: 1. Be introduced to terms presented in bold letters. 2. Learn common measurement units of the U.S. Customary (or Imperial) and International (or metric) systems. 3. Learn four scales used to measure temperature and convert between them. 4. Learn about density; state the density of air, seawater, and freshwater; and understand how water density affects diving. 5. Understand Archimedes’ principle and how to apply it to buoyancy problems. 6. Learn about pressure, distinguish gauge and absolute pressure, and determine the pressure at any depth in the ocean or in freshwater. 7. Learn about the major component gases of air and what their percentages are in normal air. 8. Learn about the several gas laws that pertain to diving and solve problems associated with them. 9. Learn about the effects of depth on a diver’s air consumption rate. 10. Learn about oxygen enriched air (nitrox). 11. Learn simple calculations of partial pressures at depth. 12. Learn about the effects of the water environment on light and sound. 13. Understand how and why a diver loses heat underwater. THE PHYSICAL WORLD The world that we know is composed of matter and energy. Matter is anything that occupies space and has mass. It is the “stuff” or substance of the universe. We think of mass as a measure of the amount of material in a body, and in everyday speech we equate it with weight. A physicist will tell you that mass and weight are not really the same, that mass is a measure of inertia, which is the resistance of a body to any change in its state of being at rest or in motion. But most of us have never been “off-planet,” so we often say weight when mass would be more precise. Remember your entrylevel scuba course; you learned that you “weigh less” when you are buoyed up by the water. On the moon you would “weigh” one-sixth what you do on earth, but in both places you would still have all of your mass. We are generally earthbound, certainly our diving is, so when we solve problems we normally use weight as the manifestation of mass in earth’s gravity. Energy is the capacity to do work. It is the force that works on and within matter. Energy can exist in several forms; potential, kinetic, thermal, mechanical, electrical, etc. Kinetic energy is the energy that a body has because it is in motion. Potential energy is stored energy that a body has because of its position. Standing on a ladder, you have potential energy relative to the Earth. You have stored energy from the work you expended to reach the top of the ladder. You will release the stored energy if you fall or jump off the ladder. Work and heat are energy in the process of being transferred. Heat is energy that is transferred between bodies as a result of their difference in temperature. We will learn more about particular forms of energy later, when we discuss heat and light. Matter is composed of atoms (figure 3-1). An atom is the smallest possible unit into which matter can be divided and still retain its unique characteristics. The idea of an atom was first developed by the early Greek philosopher Democritus of Abdera, and our word comes from the Greek word for “indivisible.” We now know that atoms are not solid and hard. They are themselves made up of more elementary particles–protons, electrons, and neutrons, but atoms are the basic chemical building NAUI Master Scuba Diver 68 Diving Physics H Atom O Atom O2 Molecule H2O Molecule FIGURE 3-1. ATOMS COMBINE TO FORM MOLECULES
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