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Unit Conversions Notes Part 1: Units and numbers Numbers with units are important in science. Units are a comparison to a standard measurement. Examples of units: Length or distance---meters, feet, centimeters, inches, miles, kilometers time---seconds, minutes, hours, days, years volume----gallons, quarts, liters, milliliters massâ€”kilograms, grams, milligrams weightâ€”pounds, oz, Newtons speed---miles/hour, feet/second, kilometers/hour When calculating with numbers and units, you must carry along the unit and do the same calculation on the unit as the number. Sometimes units are cancelled during calculations. Examples: 250 miles/ 5 hours = 50 mi/hr 60 N x 2.5 m = 150 N-m 125 g/cm3 x 100 cm3 = 12500 g 75 mi/ hr x 1.5 hr = 112.5 mi 375 lb /ft3 x 2 ft = 750 lb/ft2 Part 2: Unit Conversions We can change from one unit to another by unit conversions. A list of conversion factors is needed. Use a conversion factor like a fraction where the unit you want is on top (numerator) and the unit given in the problem is on the bottom (denominator). WANT/GIVEN Examples: 1. 79 inches to ft 1ft = 12 inches The unit we want is ft, unit given is inches 79 in (1ft/12 in) = 6.6 ft Multiply by the number in the numerator and divide by the number in the denominator the inches on the original number cancel with the inches in the bottom of the conversion fraction. 2. 29 gallons to liters 1gal=3.8 L 29 gal (3.8 L/ 1 gal) = 110.2 L 3. 5,000 mi to ft 1 mi= 5280 ft 5000 mi ( 5280 ft/1 mi) = 26400000ft 4. 275 mL to L 1L = 1000ml 275 mL ( 1L/1000mL) = 0.275 L Complex unit conversions(2 step) Complex units have numerator and denominator ex: mi/hr ft/sec g/cm3 lb/in2 Change 45 mi/hr to ft/sec Step 1--change numerator unit: want/given 45 mi/hr ( 5280ft/1 mi) =237600ft/hr Step 2---Change denominator unit: given/want 237600ft/hr ( 1hr/3600sec) =66ft/sec