Thursday, October 31, 2013 Happy Halloween! Standard IE1: Scientific progress is made by asking meaningful questions and conducting careful scientific experiments. Independent Practice: Section 3.3 Reading Packet Question: Copy the chart into your Journal. Quantity SI Base Unit Symbol Length Meter m Mass Kilogram kg Temp Kelvin K Time Second s Amount of Substance Mole mol Luminous Intensity Candela cd Electric Current Ampere A Measurements and Calculations Units of Measurement Measurements involve NUMBER and UNIT Represent a quantity: has magnitude, size, or amount Gram = unit of measurement Mass = quantity Units of Measurement Scientists system… around the world agree on one International System of Units (le Systeme International d’Unites) SI units Built from seven base units SI Base Units Units of Measurement Units of Measurement Metric Prefixes – make units easier to use Make the unit smaller or larger Unit = prefix + base unit Table pg. 74 Mass Measures quantity of matter SI unit: kilogram, kg ______ kg = _____ g gram used for smaller masses Weight: measure of gravitational pull Length SI unit: meter, m Longer distances: kilometer, km _______ km = _______ m Shorter distances: centimeter, cm _______ m = ________ cm Volume SI unit: m3 A derived unit: combination of base units by multiplying or dividing SI unit for Area: l x w = m x m = m2 Volume: l x w x h = m x m x m = m3 Also: liters (L), mL, dm3 and cm3 1 L = 1 dm3 = 1000mL = 1000 cm3 Derived Units Scientific Notation Put the numbers in the form a x 10n a has one # to left of decimal If # is bigger than 1 + exponent If # is less than 1 - exponent Scientific Notation Review: Write in scientific notation or standard notation. a. 32,700 b. 0.0003412 c. 3.901 x 10-6 d. 4.755 x 108 Let’s Practice Scientific Notation Worksheet Significant Figures (Sig Figs) How many numbers mean anything? When we measure, we can (and do) always estimate between the smallest marks. 1 2 3 4 5 Significant Figures (Sig Figs) Better marks better estimate. Last number measured actually an estimate 1 2 3 4 5 Rules for Significant Figures 1) All nonzero digits are significant. • 457 cm has 3 sig figs • 2.5 g has 2 sig figs 2) Zeros between nonzero digits are significant. • 1007 kg has 4 sig figs • 1.033 g has 4 sig figs 3) Zeros to the left of the first nonzero digit are not significant. They are not actually measured, but are place holders. • 0.0022 g has 2 sig figs • 0.0000022 kg has 2 sig fig 4) Zeros at the end of a number and to the right of a decimal are significant. They are assumed to be measured numbers. • 0.002200 g has 4 sig figs • 0.20 has 2 sig figs • 7.000 has 4 sig figs 5) When a number ends in zero but contains no decimal place, the zeros may or may not be significant. We use scientific (aka exponential) notation to specify. • 7000 kg may have 1, 2, 3 or 4 sig figs! Sig Figs What is the smallest mark on the ruler that measures 142.15 cm? 142 cm? 140 cm? Does the zero mean anything? (Is it significant?) They needed a set of rules to decide which zeroes count. Sig Figs. 405.0 g 4050 g 0.450 g 4050.05 g 0.0500060 g Sig Figs Only measurements have sig figs. Counted numbers are exact – infinite sig figs A dozen is exactly 12 Conversion factors: 100 cm = 1 m Problems 50 has only 1 significant figure if it really has two, how can I write it? Scientific notation x 101 2 sig figs Scientific Notation shows ALL sig figs 5.0 Rounding Rules Round 454.62 to four sig figs to three sig figs to two sig figs to one sig fig Sig Figs How many sig figs in the following measurements? 458 g 4085 g 4850 g 0.0485 g 0.004085 g 40.004085 g Let’s Practice Significant Figures Worksheet Journal - Thursday, November 7, 2013 Standard IE1: Scientific progress is made by asking meaningful questions and conducting careful scientific experiments. Independent Practice: Significant Figures Worksheet (#2) Question: Copy the chart into your Journal. (next slide) Prefix Meaning Factor Mega (M) 1 million times larger than unit 106 Kilo (k) 1,000 times larger than unit 103 Deci (d) 10 times smaller than unit 10-1 Centi (c) 100 times smaller than unit 10-2 Milli (m) 1,000 times smaller 10-3 than unit Micro (μ) 1 million times smaller than unit 10-6 Nano (n) 1,000 million times smaller than unit 10-9 Pico (p) 1 trillion times smaller than unit 10-12 OPEN NOTE Quiz!! When? Blocks 1 and 3: Wednesday, November 13, 2013 Blocks 2 and 4: Thursday, November 14, 2013 Topics Included: SI Units Scientific Notation Significant Figures Significant Figures in Calculations Density Conversions Vocabulary Review Calibration: a set of graduations to indicate values or positions. Precision: Describes the closeness, or reproducibility, of a set of measurements taken under the same conditions. Convey: To make something known to someone. Significant: Very important. Intervals: A period of time between events. Review: Scientific Notation and Significant Figures Worksheets Calculations with Significant Figures Rules Annotate the Reading Calculations with Sig Figs 1. 2. 3. 165.86 g + 4.091g - 140 g + 27.32 g (35.6 L + 2.4 L) / 4.083 = 2.524 x (16.408 m – 3.88 m) = Answers: 57g 9.31 L 31.62 m Let’s Practice Significant Figures in Calculations WS Density Density = mass D=m volume V Units: g/cm3 or g/mL but SI unit is kg/m3 derived unit Used to identify substances Varies with temperature As temp. increases density… Density Density Examples If a metal block has a mass of 65.0 grams and a volume of 22 cubic centimeters, what is the density of the block? D=m V D = 65.0 g = 3.0 g/cm3 22 cm3 Density Examples Aluminum has a density of 2.7 g/cm3. What volume of aluminum has a mass of 60 grams? D=M V 20 cm3 Density Examples Gold has a density of 19.3 g/cm3. A block of metal has a mass of 80 g and a volume of 12 cm3. Could this block be a piece of gold? No, because this block has a density of 7 g/cm3s Journal – Friday, November 8, 2013 Standard: IE1: Scientific progress is made by asking meaningful questions and conducting careful experiments. Independent Practice: Revise Section 3.3 Reading Packet Calculate the Following (mind your sig figs): (3.2 + 4.55) x 12.4 (88.33-6.782) / 9 Review – Sig Figs in Calculations Unit Conversions Unit Conversions 1. 2. 3. Given information in one unit need to find the equivalent in another unit Identify what’s given Organize plan of attack Carry out plan WITH UNITS!! Conversion factors ratio of equivalent measurements.” Start with two things that are the same. 1 m = 100 cm Can divide by each side to come up with two ways of writing the number 1. “A Conversion factors 1m 100 cm = 100 cm 100 cm Conversion factors 1m 100 cm = 1 Conversion factors 1m 100 cm 1m 1m = = 1 100 cm 1m Conversion factors 1m 100 cm 1 = = 1 100 cm 1m Conversion Factors Unique way of writing the number 1. Does NOT change the VALUE, it changes the UNITS. Write the conversion factors for the following kilograms to grams feet to inches 1 L = 1 dm3 = 1000mL = 1000 cm3 Method for Converting 1. 2. T-Chart or Factor Label Method Steps: 1. 1. Draw a Great Big “T” 2. 2. Put the number the problem gives you to convert to the top left of the “T”. 3. 3. Put the unit of that number in the bottom right part of the “T”. 4. 4. Write the units of what you want in the top right. 5. 5. Write the unit conversion factor in front of the units from Steps 3 and 4. Let’s Try Some! 323 mm = _____ nm 3.2 miles = _____ in 250 gallons = _____ mL 15 days = _______ min More Unit Conversions More Involved Derived Unit Conversions 54.3 cm3 = ______ m3 7.54 ft2 = _______ in2 Derived Unit Conversions 125.3 m/s = ______ mi/hr 625 g/mL = ______ kg/m3 100 km/hr = ______ mi/hr Let’s Practice Dimensional Analysis Where do these measurements come from? Recording Measurements Making Good Measurements 1. We can do 2 things: Repeat measurement many times - reliable measurements get the same number over and over - this is PRECISE Making Good Measurements 2. Test our measurement against a “standard”, or accepted value - measurement close to accepted value is ACCURATE Measurements are Uncertain 1. 2. 3. 4. Measuring instruments are never perfect Skill of measurer Measuring conditions Measuring always involves estimation Flickering # on balance Between marks on instrument Estimating Measurements Error Probably not EXACTLY 6.35 cm Within .01 cm of actual value. 6.35 cm ± .01 cm 6.34 cm to 6.36 cm Calculating Percent Error Compares your measurement to accepted Valueexperimental -Valueaccepted value Percentage error = × 100 Valueaccepted Negative if measurement is small Positive if measurement is big Calculating Percent Error What is the % error for a mass measurement of 17.7g, given that the correct value is 21.2g? Let’s Practice Percent Error Worksheet