Hand in Course Outline, Safety Agreement, Contact Lens Letter on the overhead please New students: measurement lab at lunch today, safety quiz tomorrow at lunch Was it helpful to post up the notes a day beforehand? I will try to do this a the night before every class I ask you to take notes Dimensional Analysis (Unit Conversions) Conversion Factors Same Quantity, Different Units Sig Figs in Conversion Factors Exact/Defined/Counting Numbers Warning: not all conversion factors are exact Can you think of an example of an inexact conversion factor? Exact/Defined/Counting Numbers Warning: not all conversion factors are exact Can you think of an example of an inexact conversion factor? Conversions between metric & imperial units E.g. 1 m = ft This number is rounded to 6 sig figs but goes on forever There is uncertainty so the number of sig figs matter Exact or Inexact? 28 students in the classroom $20.48 in my pocket 100,000 hairs on my head Solving Unit Conversion Problems Step 1: identify the initial amount what info are you given? Step 2: identify the unknown amount what are you looking for? Step 3: identify the conversion factor how are 1 & 2 related? Overall: unknown amount = initial amount x conversion factor Example 1 How many min are there in 3480 s? Step 1: Step 2: Step 3: Example 1 How many min are there in 3480 s? Step 1: initial = 3480 s Step 2: Step 3: Example 1 How many min are there in 3480 s? Step 1: initial = 3480 s Step 2: unknown = min Step 3: Example 1 How many min are there in 3480 s? Overall: unknown = initial x conversion factor Example 1 How many min are there in 3480 s? Overall: unknown = initial x conversion factor ? min = 3480 s x conversion factor Want to leave min and cancel s so use the c.f. with min on top (numerator) and s below (denominator) Example 1 Example 2 (dont copy, just try) The automobile gas tank of a Canadian tourist holds L of gas. If 1 L of gas is equal to gal in the US (gal is the symbol for gallon), and gas is $1.26/gal in Dallas, Texas, how much will it cost the tourist to fill his gas tank in Dallas? Example 2 Initial = Unknown = Conversion factors: Example 2 Initial = L Unknown = Conversion factors: Example 2 Initial = L Unknown = $ (cost) Conversion factors: Example 2 Initial = L Unknown = $ (cost) Conversion factors: L gal: gal $: Example 2 Unknown = initial x c.f. x c.f. Example 2 $ ? = L x c.f. x c.f. First c.f. must cancel out litres Must have L in the denominator (below) Example 2 Tips to Avoid Rounding Errors Write only one equation for the entire question If you must do more than one equation, do not round before you get to the final answer Instead, write down as many digits as you can or use the memory function on your calculator (M+) This is the difference b/t right and wrong answers! SI Units The International System of Units (Le Systme International dUnits) Modernized version of the metric system used in science Any SI prefix can be used with any SI base unit SI Base UnitsSI Prefixes Quantity Unit name Unit Symbol Lengthmetrem Masskilogramkg VolumelitreL Timeseconds TemperatureKelvinK Amount of Substance molemol Written Prefix Prefix Symbol Equivalent Exponential megaM10 6 kilok10 3 hectoh10 2 dekada decid10 -1 centic10 -2 millim10 -3 micro10 -6 SI Prefixes 5 Mm = 5x10 6 m 5 m = 5x10 -6 Mm 12 ms = 1.2x10 -3 s 12 s = 1.2x10 3 ms Written Prefix Prefix Symbol Equivalent Exponential megaM10 6 kilok10 3 hectoh10 2 dekada decid10 -1 centic10 -2 millim10 -3 micro10 -6 Other Units & Equivalences 1 t = 1 tonne = 10 3 kg 1 mL = 1 cm 3 (cubic centimetres, cc) 10 3 L = 1 m 3 Derived Units A unit made by combining two or more other units Speed = distance/time = km/h Density = mass/volume = g/L Practice Hebden p #2-40