3A major theme of science is communication and collaboration A major theme of science is communication and collaboration. We need a single measurement system for everyone.Le Systeme International d’Unites - SI
4SI UNITS Quantity Unit Name Abbreviation Length Meter m Mass Kilogram kgTimeSecondsTemperatureKelvinKAmount of substanceMolemolElectric currentAmpereALuminous intensityCandelacd
5We use SI prefixes to represent quantities that are larger or smaller than the base units.
6PrefixAbbreviationConversiongigaG1 Gm = 109 mmegaM1 Mm = 106 mkilok1 km = 1000 mhectoh1 hm = 100 mdecada1 dam = 10 m1 meter (1 m)decid1 m = 10 dmcentic1 m = 100 cmmillim1 m = 1000 mmmicroμ1 m = 106 μmnanon1 m = 109 nm
7Dimensional AnalysisDimensional Analysis is a method used to make conversions. This method helps us organize information without becoming confused about what units are being cancelled or multiplied/divided.
8Everything on bottom is divided from the top RulesYou must use Dimensional Analysis to solve conversion problemsAlways show all your workInclude unitsMake sure your units cancel outEverything on the top is multipliedEverything on bottom is divided from the top
9Conversion FactorsA ratio (or fraction) derived from the equality between two different units that can be used to convert from one unit to the other.Conversion factors always equal one because the two values are equal to each other.
10Conversion Factors 4 quarters 1 dollar = 1 = 1 1 dollar 4 quarters 60 minutes1 hour= 1= 11 hour60 minutes1 m100 cm= 1= 1100 cm1 m
11Convert 62.0 inches to centimeters First we need to map out what we are doing.62.0 in ___ cm
12Convert 62.0 inches to centimeters Second we need to determine our conversion factorHow many centimeters are in one inch?2.54 cm = 1 in1 in2.54 cmNote: We could have also used that 1cm = .394 inch but as a general rule, the larger unit gets the 1!= 1= 12.54 cm1 in
13Convert 62.0 inches to centimeters Third, we multiply our given by the conversion factor…making sure to arrange the conversion factor so that the units CANCEL!62.0 in2.54 cmX= cm1 inNote: Units that are both on the top and the bottom cancel
14Convert 62.0 inches to centimeters Lastly, we make sure that we reached our “destination” and that we have the correct number of significant figures.cm 157 cmNote: Conversions factors do not follow significant figure rules, they are not measured and do not show accuracy.
15Multiple ConversionsWhen conversions require several steps, Dimensional Analysis is extremely useful. It helps organize information so we can think through problems step-by-step.
16How many feet are in 965 cm? 1. Map it out: 965 cm ___ ft 2. Find conversion factors:
18How many feet are in 965 cm? 965 cm 1 in 1 ft X X = 31.66 31.7 ft
19You are cooking for a large group of people You are cooking for a large group of people. You must change the recipe to accommodate all the guests. How many gallons will 384 teaspoons of vanilla extract occupy?1 Tablespoon (T) = 3 teaspoons (t)1 cup (c) = 16 Tablespoons1 pint (pt) = 2 cups1 quart (qt) = 2 pints1 gallon (gal) = 4 quarts