from hands-on chemistry
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1.2.1 THE IMPORTANCE OF UNITS3
1.2.2 UNITS IN CHEMSITRY6
1.2.3 PROBLEM SOLVING (dimensional analysis)11
FOR THE TEACHER15
1.2.1 THE IMPORTANCE OF UNITS16
1.2.2 UNITS IN CHEMISTRY17
1.2.3 PROBLEM SOLVING (Dimensional Analysis)19
An accurate and consistent system of measurement is the foundation of a healthy economy. In the United States, a carpenter pays for lumber by the board-foot, while a motorist buys gasoline by the gallon, and a jeweler sells gold by the ounce. Land is sold by the acre, fruits and vegetables are sold by the pound, and electric cable is sold by the yard. Without a consistent, honest system of measurement, world trade would be thrown into chaos. Throughout history, buyers and sellers have tried to defraud each other by inaccurately representing the quantity of the product exchanged. In the Bible we read that the people of Israel were commanded to not "...use dishonest standards when measuring length, weight or quantity" but rather "use honest scales and honest weights..." (Leviticus 19:35-36). From ancient times to the present there has been a need for measuring things accurately.
When the ancient Egyptians built monuments like the pyramids, they measured the stones they cut using body dimensions every worker could relate to. Small distances were measured in "digits" (the width of a finger) and longer distances in "cubits" (the length from the tip of the elbow to the tip of the middle finger; 1 cubit = 28 digits). The Romans were famous road builders and measured distances in "paces" (1 pace = two steps). Archaeologists have uncovered ancient Roman roads and found "mile"-stones marking each 1000 paces (mil is Latin for 1000). The Danes were a seafaring people and particularly interested in knowing the depth of water in shipping channels. They measured...