NAUI Master Scuba Diver 74 Diving Physics Units of volume/capacity include: SI/metric 1 liter = 1,000 milliliters (ml) 1 milliliter = 1 cubic centimeter (cc or cm3) U.S./Imperial (liquid measure) 16 fluid ounces = 1 pint 2 pints = 1 quart 4 quarts = 1 gallon 1 U.S. gallon = 231 cubic inches (exactly) 1 Imperial gallon = 277.4 cubic inches 1 cubic foot (ft3) = 7.48 U.S. gallons Conversions 1 liter = 1.06 U.S. quarts 1 liter = 0.0353 ft3 1 ft3 = 28.316 liters Conversion problems: 1. What is the internal volume in cubic feet of a 12 liter (water capacity) scuba cylinder? Answer: 12 liters x 0.0353 ft3/liter = 0.424 ft3 2. How many liters are in a U.S. gallon? Answer: 1 gallon x 1 ft3 x 28.316 liters = 3.79 liters 7.48 gallons 1 ft3 Here again, it was a two step process, first converting gallons to cubic feet, then converting cubic feet to liters. Weight (Mass) Remember that in general use we do not rigorously distinguish between mass and weight, and we tend to use the terms interchangeably. Generally, “weight” will mean the weight of an object in air, even though air provides some small amount of buoyancy. The standard unit of mass in the SI/metric system is the kilogram. The kilogram (kg) is the only SI unit that still has a physical object as its standard. It is the mass of a prototype platinum-iridium cylinder kept at Sevres in France. It is also the only basic unit of measurement that already has the prefix kilo in place. The kilogram is approximately equal to the mass of one liter of pure water at 4° Celsius. In the U.S./Imperial system, the standard unit of mass is the pound (lb). The pound is a traditional weight that originated in Europe in the Middle Ages. It is sometimes called an avoirdupois pound to distinguish it from the lighter troy pound, which is used only for measuring precious metals and medicines. Since 1959 the pound has been defined by reference to SI measure as 0.45359237 kg. Units of mass/weight include: SI/metric 1 kilogram (kg) = 1,000 grams (g) 1 gram = 1,000 milligrams (mg) 1 kilogram = 1,000,000 milligrams 1 metric ton = 1,000 kilograms U.S./Imperial 1 pound = 16 ounces 1 stone (U.K.) = 14 pounds 1 ton (U.S. or short ton) = 2,000 pounds 1 ton (U.K. or long ton) = 2,240 pounds Conversions 1 kilogram = 2.2 pounds 1 pound = 453.59 grams Temperature Temperature is the measure of hotness or coldness. Heat and temperature are related, but they are not the same. Heat is a form of energy, and temperature is a measure of the amount of heat energy present. There are four temperature scales in use today (figure 3-3). The Celsius temperature scale and the Fahrenheit temperature scale are the two in common usage. In the early eighteenth century Daniel Gabriel Fahrenheit, a German physicist, devised a practical temperature scale. For his zero-degree point Fahrenheit chose the temperature of an ice-salt mixture, the coldest temperature he could reproduce in the laboratory. On the Fahrenheit temperature scale there is an interval of 180 degrees between the freezing point and boiling point of water. Water freezes at 32°F and boils at 212°F. The Fahrenheit scale is still used in the United States. In 1742, the Swedish astronomer Anders Celsius proposed a temperature scale with 0° for the freezing point of water and 100° for the boiling point of water. Until recently, the Celsius scale was known as the centigrade scale because of its 100-degree interval between the phase transition temperatures of water. The Celsius temperature scale is the one used in most of the world.
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