FACTOR LABEL METHOD• A method of converting units from one form to another. • Must have a conversion factor to perform factor label method that is arranged so that like units cancel.• Significant figures still matter • Our final answer will have the same # of sig figs as the number we are converting
CONVERSION FACTOR • Used to convert a measured quantity to a different unit of measure without changing the relative amount. • It is a ratio (fraction) that equals one • Examples: • 1 inch = 2.54 cm => 1 inch/2.54cm • Aka a bridge • See first page in text for unit conversion factors
EXAMPLE: LET’S START OFF EASY…• Let’s say we want to find out how many centimeters are in 21.5 inches1. Identify information wanted & information given 21.5 inches = ?? Centimeters2. Identify unit conversion(s) to be used 2.54 cm = 1 inch3. Arrange conversion factor as shown: **only true if our desired units do not have a unit in the denominator** Desired units Original units4. Multiply the numbers in the numerator, and the numbers in denominator5. Divide the numerator by the denominator
FACTOR LABEL METHOD • Converting 21.5 inches to centimeters: • Conversion Factor: 2.54 cm 1.00 in.
EXAMPLE: LET’S MAKE THINGS A BITTRICKIER…• Ex: how many hours are there in 7200 seconds? 1. Identify information wanted & information given 7200 sec. = ?? hours2. Identify unit conversion(s) to be used 60 sec = 1 min 60 min = 1 hour3. Arrange conversion factors as shown: Desired units Original units4. Multiply so that units cancel
FACTOR LABEL METHODEx: how many hours are there in 7200 seconds?1. 7200 sec. = ?? hours2. 60 sec = 1 min 60 min = 1 hour3 & 4. 7200 sec. x 1 min x 1 hour = 2 hrs 60 sec 60 min
EXAMPLE: YOUR TURN!Try this one: How many inches are in 1.00 miles?1. Identify information wanted & information given2. Identify unit conversion(s) to be used1. Arrange conversion factor as shown: Desired units Original units4. Multiply so that units cancel
EXAMPLEHow tall are you…- In inches?- In meters?- In miles?
EXAMPLE: CONVERTING RATES• What is 65 miles per hour converted to feet per second? • NOTE: the word “per” identifies that there is a ratio • Rewrite as 65 miles and feet hour sec
EXAMPLE: THE MORE DIFFICULT STUFF!What is 65 miles per hour converted to feet per second?1. Identify information wanted & information given1. Identify unit conversion(s) to be used1. Arrange conversion factors so that desired units are left2. Multiply so that units cancel
FACTOR LABEL METHOD • This method can also be used to convert between metric unit prefixes • Ex: how many meters are in 52 cm? 52 cm x 1.0 m = 0.52 m 100 cm • You should memorize all metric conversions from kilo through milliprefix mega kilo hecto Deka Deci Centi Milli micro Meter Gram Value 106 103 102 101 Second 10-1 10-2 10-3 10-6 Liter mAbbrev- g M k h da d c m μ (“mew”) iation s