Presentation on theme: "Chapter 2: Measurement and Calculations"— Presentation transcript:
1 Chapter 2: Measurement and Calculations Key concepts:Differentiate between accuracy and precisionApply principles of measurement andsignificant figuresIdentify and use the 7 base SI unitsName and apply units of measurePerform unit conversionsCalculate densityCalculate percent error
2 A. Accuracy vs. Precision __________ - How close you are to the correct measurement or calculation based on the standard value.PRECISION__________ - How close your measurements are to EACH OTHERThe density of aluminum is 2.78 g/cm3.Bob calculates the density three times and gets 2.75, 2.79 and 2.77.AVG: 2.77Mary calculates the density three times and gets 4.66, 4.67, and 4.65AVG: 4.66Holden calculates the density three times and gets 10.25, 6.87, and 1.25AVG: 6.12Franz calculates the density three times and gets 2.90, 1.95, 3.44AVG: 2.76ACCURATE AND PRECISEPRECISE BUT NOT ACCURATENIETHER ACCURATE NOR PRECISEACCURATE BUT NOT PRECISE
3 B. Measurement Measurement ___________ Something with magnitude, size oramount.Unit________ - Compares what is measured to adefined size.Metric________ - Standard system of measure usingbase 10.SI________ - The international system of measurethat uses only BASE metric units
4 B. Measurement Quantitative ___________ - Measurements having numbers orsize.Qualitative___________ - Measurement having subjectivedescriptionsExamples:20 ml of waterThe reaction bubblesUma Thurman is blonde17 g/mlBulldogs are #1QUANTITATIVEQUALITATIVEQUALITATIVEQUANTITATIVEQUALITATIVE
5 C. Significant figuresSignificant figures indicate the accuracy of the measuring instrument.2.35 cmLast digit is ESTIMATEDNot possible to estimate ; can only estimate between graduations
6 C. Significant figures Consider the following: What’s the estimate? This ruler isn’t as accurate as the previous.
7 C. Significant figuresRULEEXAMPLENO. OF SIG FIGSAll nonzero digits and zeros between those digits are significant1 458 g40.7 mmmLeading zeros with decimal points are NOT significant; Ending zeros ARE significant with decimalkgmLmEnding zeros left of the decimal point may or may not be significant. Indication needed.kgkg1.50E4 kg1.500E4 kg43714662534Scientific notation is always in sig fig form
8 C. Significant figures ADDITION AND SUBTRACTION Answer has as many DECIMAL POINTS as the part with the LEAST decimals.5.44 – = – == =2.832.8294-13.4-13.422.1560.40.358
9 C. Significant figures MULTIPLICATION AND DIVISION Answer can only contain as many SIG FIGS as the part with the LEAST sig figs8.15 x 6 = / 0.87 =1.2 x 1010 = / 1.50 =48.9500.291200121211.4
10 C. Significant figuresHow about this one: (not in your notes; use calc)20
11 Scientific researchers use ONLY these units! D. SI base unitsQuantityUnitAbb.MetermLengthMassKilogramkgTimeSecondsTemperatureKelvinKAmount of substanceMolemolE. CurrentAmpereALuminous intensitycandelacdWe won’tScientific researchers use ONLY these units!
12 D. SI Base units cont. Derived units – Made up of the base units QuantitySI UnitOther UnitsAreaVolumeDensitySpeedEnergyacres, cm2, ft2m2m3L, gal, cm3mi/hr, ft/sCalorie, kWhr
13 E. Unit Conversions – metric prefixes kilohectodecaunitdecicentimillikinghectorDoesn'tUsuallyDrinkChocolatemilkEXAMPLES1 000g = ________ Kg dam = _______ mm0.23 Kg =________ dg cL = ________ HL345 DaL = _____ Km Km = ___________ mm
14 F. Metric conversions – conversion factors All conversions start with an EQUALITY1 inch is the same as 2.54 cm1 inch = 2.54 cmEqualities are turned into conversion factors:Notice the top and bottom are same length!
15 F. Metric conversions – conversion factors Convert 34 inches to centimeters2.54cm34 in86.36 cm1inConversion factor goes here
16 F. Metric conversions – conversion factors MULTI- STEPThe Bulldogs need 550 cm for a first down. How many yards is that?Plan: cm inch feet yardsyd1in1ft1550 cm6 yards2.54cm12in3ft
17 F. Metric conversions – conversion factors A baseball is thrown 60 ft/s. How fast is this in miles/hour?Two things to convert. Do one at a time.1. ft miles2. s min hours1mi60s60min40.91 mi/hr5280ft1min1hr
18 F. Metric conversions – powered units Misconception: 1 m = 100 cm but1m3 ≠ 100 cm3So, 100x100x100 = 1,000,000 cm31 m3 cube1 m100 cmIf the unit is cubed, you cube the numbers too1 m(1 m)3 = (100 cm)3100 cm1 m1 m3 = 1,000,000 cm3100 cm
19 F. Metric conversions – Volumes 1 ml = 1 cm3Critical equality:How many liters of fuel does a 300 m3 tank hold?11,000,000cm31mlL300 m3300,000 L11mlm3cm31,000Or you could do King Hector
20 F. Metric conversions - Temperature 180 Fo = ? KThou shalt use:Work:
21 G. DensityMeasure of how tightly packed matter is.More dense
24 G. Density, cont. Units: When measuring LxWxH When measuring Volume w/ cylinder
25 G. Density, cont.A liquid has a density of 0.87 g/mL. What volume is occupied by 25 g of the liquid?Given:Work:D = 0.87 g/mLV = ?M = 25 g
26 H. Percent Error %E = Percent error Va = Accepted value Ve = Experimental valueExample:A student measures the density of a solid as 3.42 g/cc. The solid really has a density of 3.76 g/cc. Calculate the percent error. cc = cubic centimeterVa = 3.76 g/cc Ve = 3.42 g/cc
27 Watch parentheses here!!! H. Percent Error, contGiven:Work:Va = 3.76 g/cc Ve = 3.42 g/ccWatch parentheses here!!!%E =%E = 9.04% (sig figs)You can ignore negative signs. A positive percent means the accepted value is higher than your value. A negative means it’s lower.