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Scientific MeasurementScientific Measurement
David Chan
Northwestern UniversityAdd Add
CorporateCorporateLogoLogoHereHere
Today (Day Eight)Today (Day Eight)
• (0-15) Discuss Test (0-15)• (15-20) Discuss Test Resubmittal Process (15-20)• Chapters 2+3 Syllabus• (20-35) Qualitative vs. Quantitative (20-35)• Accuracy vs. Precision• (35-43) Class Jobs• (0-15) Website intro, online grades• (15-30) Scientific Notation (35-43) • (30-43) Popsicle sticks match game
Scientific Measurement Scientific Measurement
• Questions to Ponder:– Why is measurement important?– What are the different types of
measurement? – What is the history of measurement?– What do you know already?– What do you think we will focus on when
studying measurement?
Types of MeasurementsTypes of Measurements
Types of MeasurementsTypes of Measurements
3
1406
350
868
Types of MeasurementsTypes of Measurements
Types of MeasurementTypes of Measurement
Types of MeasurementsTypes of Measurements
• Qualitative Measurements– Descriptive, nonnumerical form
• Quantitative Measurements– Definite form, numbers and units
• Examples: – Basketball is brown – Diameter of basketball is 31 cm – Air pressure in the basketball is 12 psi. – Surface of basketball has indented seams.
Accuracy, Precision, and ErrorAccuracy, Precision, and Error
• Accuracy – how close to actual or true value• Precision – how close measurements are to one another• Dartboard analogy• Examples
– Precision or accuracy?• Multiple measurements • Correct • Repeatable • Reproducible • Single Measurement • True value
Converting Measurements to Scientific NotationConverting Measurements to Scientific Notation
• Useful for large and small numbers• 2 numbers: Coefficient + 10 raised to power• Addition and Subtraction
– Exponents must be same to add coefficients• Multiplication
– Multiply coefficients and add the exponents• Division
– Divide coefficients and subtract exponents• EE button on calculator• Practice Problems #4
Examples: Examples:
– 91.4m– 0.000000000154 m– 6378000 m– 0.000008 m– 149600000000 m
Today (Day Nine)Today (Day Nine)
• (0-15) Cat’s Meow – qualitative observations• (15-25) Significant Figures
– Paper rulers• (25-35) SI Units – Length, Volume, Mass• (35-43) Discuss HW – clock buddies
Significant FiguresSignificant Figures
• Important when making measurements in experiments
• All digits known with certainty plus one estimated or uncertain digit
Rules/ExamplesRules/Examples
• 1) 24.7m (3)• 2) 7003 m (4)• 3) 0.0071 m (2)• 4) 25.0 (3) • 5) 27,210 m (4)
Rules ExplainedRules Explained
• 1) Nonzero digits are always significant (24.7m)• 2) Zeroes in between are significant (7003m)• 3) Left zeroes are not significant (0.0071 m)• 4) Right zeroes are significant (25.0 m)• 5) Right zeroes left of understood decimal are not sig.
(27,210m)• 6) Unlimited sigfigs
– Counting, exact quantities (60min=1hr)• Practice Problems #5,6
More RulesMore Rules
• Rounding: answers cannot be more precise than least precise measurement from which it was calculated
• Rounding: greater than 5, less than 5• Add/Subtract: round to least significant place• Mult/Divide: round to same # as least number of
sigfigs• Practice Problems #11,12
SI units and PrefixesSI units and Prefixes
• International System of Units (SI)• SI Base Units (table 2.1)
– Length, Mass, Temp, Time• SI Unit Prefixes
– Table 3.3• Derived Units
– Density, volume
LengthLength
• Basic SI unit = meter• Common: millimeters, centimeters, kilometers• Running races: 5K, 10K
VolumeVolume
• Derived unit: cubic _____meters• CC’s = cubic centimeters• 1 CC = 1ml• 1 cubic decimeter = 1L• Volumetric flasks, graduated cylinders
Mass vs. WeightMass vs. Weight
• Mass – amount of matter (1 kg)• Weight – force on mass by gravity (Physics)
Today (Day 10)Today (Day 10)
• (0-5) Opener – sci notation• (5-15) Density• (15-20) Density Demo: How Sweet It is!• (20-25) Temperature
– Making thermometers?• (25-30) Percent Error
– Activity• (30-35) Discuss HW – clock buddy
Calculating DensityCalculating Density
• Density = Mass/Volume• Characteristic of substance• Water displacement technique• Temperature increases, V increases, Density decreases• Density of Common substances (table 2.8)• Practice Problems #23,24• Examples:
– Volume = 245 cm3 and mass of 612 g. Is it aluminum?– density of gold = 19.3 g/cm3. What is volume of 5-g sample?– Plastic ball with volume of 19.7 cm3 has a mass of 15.8 g.
Sink or float in gasoline (0.67g/cm3)?
Specific GravitySpecific Gravity
• Comparison of density of substance with density of reference, usually at same temp.
• Specific Gravity = density of substance/density of water
Converting Celsius and KelvinConverting Celsius and Kelvin
• Temperature– Determines direction of heat transfer
• Thermal expansion – Generally expand as temp increases– Generally contracts as temp decreases
• Celsius – history• Kelvin = -273.15 C = 0 K
– Accounts for absolute zero (-273.15C)• Examples
– 170 Celsius to Kelvin– 87 K to Celsius
Percent Error, Experimental ErrorPercent Error, Experimental Error
• Accepted value – correct value established by references
• Experimental Value – measured in lab• Error: accepted – experimental• Percent Error: error/accepted x 100%• Example
– Estimated volume = 200 mL– Accepted volume = 208 mL Calc Percent error
Today (Day 11)Today (Day 11)
• (0-10) Discuss HW – jigsaw (0-10)• (10-15) Class Jobs (10-15)• (15-20) How to Write Lab Reports, Sample
Reports (15-20)• (20-30) PreLab: Observing Chemical Changes
– 4 more safety rules • (30-43, 0-20) Lab: Observing Chemical Changes• (20-43) Prep Debate (20-43)
Today (Day 12)Today (Day 12)
• (0-5) discuss HW answers• (5-10) Review Debate • Reading Volumes Demo• (10-40) Debate • (40-43) Review for Quiz
Today (Day 13)Today (Day 13)
• (0-10) Opener – sigfig/equipment activity• (10-15) Review Debate/Labs – Peer review• (15-20) Demo – Can You Pour a Gas?• (20-35) Quiz • (35-43) PreLab• (0-43) Lab – Density
POURING CARBON DIOXIDE.
• Construct a series of three 5-cm steps that will fit into a wide mouth jar. Set a lighted candle on each step. Slowly pour carbon dioxide gas from an open container into the jar. Carbon dioxide is heavier than air. As it settles it extinguishes the candles one by one starting with the candle at the lowest level. There are many ways to generate carbon dioxide. Try mixing some vinegar with bicarbonate of soda. [HG]
Today (Day 14)Today (Day 14)
• (0-10) discuss quiz• (10-20) Discuss lab• (20-35) Problem Solving• Conversion Factors - list• (35-43) Powers of Ten Website/Video• Converting between units
Dimensional Analysis – Converting UnitsDimensional Analysis – Converting Units
• Write starting quantity• Write conversion factors
– Numerator: What are you trying to convert into?
– Denominator: What are you converting from?– Which one is bigger? = 1– How many does it equal?
• 1 m = 100 cm• 1000 m = 1 km
List of Unit PrefixesList of Unit Prefixes
• Powers of ten Java– http://micro.magnet.fsu.edu/primer/java/sci
enceopticsu/powersof10/• List of 20:
– http://physics.nist.gov/cuu/Units/prefixes.html
• Common ones:– http://lamar.colostate.edu/~hillger/common.
htm• Prefixes revisited
– http://www.wordwizz.com/pages/10exp0.htm
PracticePractice
– 0.044 km to meters– 860 mg to grams– 6.7 s to milliseconds
Today (Day 15)Today (Day 15)
• (0-5) Opener• (5-10) Discuss HW• (10-15) Multistep, Complex Units• (15-43) Stations Activity – Converting Units
Multistep ProblemsMultistep Problems
• Use more than one conversion factor• Examples:
– 261 nm to millimeters– 642 cg to kilograms
Complex UnitsComplex Units
• Areas, Volumes, Speeds• Examples:
– 55 mph to m/s– 1.54 kg/L to grams per cubic centimeter
Today (Day 16)Today (Day 16)
• Peer Review – Density Labs (20 min)• Review for Test (30-40 min)
Today (Day 17)Today (Day 17)
• Test (40-60 min)
Intro to LabsIntro to Labs
• Lab Report Format• Lab Safety• Lab Notebooks• Lab Preps
Lab #1: Chemical and Physical ChangesLab #1: Chemical and Physical Changes
• Objectives: – Chemical and physical properties– Chemical and physical changes– Become acquainted with lab facilities
• Lab Techniques:– Filtration/Evaporation– Bunsen Burners– General Lab Procedures:
• Supplies/Cleaning• Contamination of materials• Dissolving small quantities
• Lab Analysis Questions– All (#1-6) except last two questions (Going Further)
Exit SlipsExit Slips
• On a separate sheet of paper labeled “Exit Slip”, please include the following:
• 1 thing you learned today• 1 thing that still confuses you• Any other comments about the pace, methods, etc.• Thank you!