Chapter 3- Diving Physics Diving Physics 73 Length The unit of length in the SI/metric system is the meter (m). In the original metric system this was 1/10,000,000 of a quadrant of the meridian passing through Paris. In the SI a meter is defined as the distance light travels through a vacuum in 1/299,792,458 second. The unit of length in the U.S./Imperial system is the foot. Probably originally based on the length of a medieval king’s foot, it was defined by legislation in the U.S. as 0.3048 meter in 1959. Units��of��length��include: SI/metric 1��millimeter��(mm)��=��0.001��meter 1��centimeter��(cm)��=��0.01��meter 1��kilometer��(km)��=��1,000��meters U.S./Imperial 1��foot��=��12��inches 1��yard��=��3��feet 1��fathom��=��6��feet 1��statute��mile��=��5,280��feet 1��nautical��mile��=��6,076.115��feet��(1,85����meters;��the traditional��nautical��mile��is��equal��to��one��minute of��arc��on��the��equator��of��the��earth)��Conversions 1��foot��=��0.3048��meter��(exactly) 1��inch��=��2.54��centimeters��(exactly) 1��mile��=��1.609��kilometers 1��meter��=��39.37��inches Conversion��problems: 1. How many meters are in 66 feet? Answer: There are 0.3048 meters per foot. So: 66 feet x 0.3048 m/foot = 20.1 meters 2. How many miles are in a kilometer? Answer: There are 1.609 kilometers per mile, So: 1 km ÷ 1.609 km/mile = 0.622 mile Or, if you only remember how many centimeters are in an inch, apply several conversion factors serially: 1 kmx 1,000mx 100 cm x 1 inch x 1 foot x 1 mile = 0.621mile 1 km 1 m 2.54 cm 12 inches 5,280 feet Notice how all of the intermediate units cancel out as you solve the problem. Also, there are two different answers (differing by one-thousandth of a mile), because 1.609 km/mile is an approximate equivalent, while 2.54 cm/inch is an exact equivalent. Area Both the SI/metric system and the U.S./Imperial system use units of length squared to measure area (length x width). In the SI/metric system it is a matter of moving the decimal point twice as many places as in measuring length. In the U.S./Imperial system one must either memorize equivalents or perform the multiplication. 1 square meter = 100 x 100 square centimeters = 10,000 square centimeters 1 square yard = 36 x 36 square inches = 1,296 square inches Both systems have special units for measuring land area. In the SI/metric system, an are is 100 square meters. This is inconveniently small, so a hectare, or 10,000 square meters, is the usual measure. In the U.S./Imperial system, an acre is 43,560 square feet (160 square rods or 1/640 square mile). Volume Volume is the measure of the space occupied, and capacity is the measure of the volume that can be contained. Volume and capacity are expressed in units of length cubed (length x width x height). The unit of volume in the SI/metric system is the cubic meter, but the smaller liter (cubic decimeter) is the common usage term. The abbreviation for liter can be either “l” or “L,” but “L” is preferable if there is a possibility of confusion with the numeral “1.” Conversions within the SI/metric system are a matter of moving the decimal three times as many places as in converting units of length. In the U.S./Imperial system, one must perform the multiplication. In addition, the common units of volume in the U.S./Imperial system have no simple relationship to cubic foot measurements, and conversion factors must be applied. Also, the common units in the U.S. customary system and the British Imperial system (gallons, pints, etc.) are not the same size, and moreover the U.S. dry measure is not the same as the U.S. liquid measure.
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