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Scientific MeasurementScientific Measurement

David Chan

Northwestern UniversityAdd Add

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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!