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Unformatted text preview: Unit Conversion Using the Factor Label Method Objective: Develop a proficiency in converting the units for a system using the factor label method. Introduction: In lab this year many of the experiments involve measuring some property of a substance (quantitative analysis) or combining known quantities of materials in a chemical reaction (synthesis). In both types of lab work you will need to be able to express amounts in a variety of units. Often beginning scientists will record only numbers in their lab notebook. This is a terrible idea and not allowed in any chemistry lab you will ever perform. All numbers you record will have some units associated with them. The unit is in fact more important than the number. During a family vacation Dennis, tired of the ride, asked his mother how much longer they had to drive. Luckily the family was nearing their destination and the mother told Dennis they had seven miles to go. He immediately counted, “1, 2, 3, 4, 5, 6, 7” and announced loudly, “Seven, we are there now. Stop the car.” Mom looked in the review mirror at him and answered, “Seconds are not the same units as miles.” We know that time and distance are not the same units, but they are related. In this case they are related by how fast the car is traveling, the speed. Typical units for speed are miles per hours (mi/hr). In this case Dennis’ family was traveling 60 mi/hr. Mom thought, “What number should Dennis count up to for these last seven miles to pass?” Mom needed to convert miles into seconds. She might have thought something like this. 60 mi/hr is close to 1 mile/minute, and in a minute my son can count to eighty. So she did the math: For good measure Mom told Denis that in this case seven miles was the same as counting to six hundred. Dennis didn’t quite make it to six hundred, but this unit conversion did kill some time for the bedraggled Mother. Today in lab we will investigate several examples of unit conversion using a process called the factor label method. This is a technique that will be used with regularity in this and other science courses. 1. Proportional Reasoning: The figure below is a useful example of proportional reasoning. The height of a tall tree can be measured by knowing the length of the shadow cast by the tree and a relationship (proportion) between tree height and shadow length. between tree height and shadow length....
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 Spring '09
 International System of Units, Kilogram, Conversion of units

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