Presentation on theme: "Chapter 2: Measurement and Calculations"— Presentation transcript:
1Chapter 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
2A. 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
3B. 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
4B. Measurement Quantitative ___________ - Measurements having numbers orsize.Qualitative___________ - Measurement having subjectivedescriptionsExamples:20 ml of waterThe reaction bubblesUma Thurman is blonde17 g/mlBulldogs are #1QUANTITATIVEQUALITATIVEQUALITATIVEQUANTITATIVEQUALITATIVE
5C. Significant figuresSignificant figures indicate the accuracy of the measuring instrument.2.35 cmLast digit is ESTIMATEDNot possible to estimate ; can only estimate between graduations
6C. Significant figures Consider the following: What’s the estimate? This ruler isn’t as accurate as the previous.
7C. 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
8C. 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
9C. 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
10C. Significant figuresHow about this one: (not in your notes; use calc)20
11Scientific researchers use ONLY these units! D. SI base unitsQuantityUnitAbb.MetermLengthMassKilogramkgTimeSecondsTemperatureKelvinKAmount of substanceMolemolE. CurrentAmpereALuminous intensitycandelacdWe won’tScientific researchers use ONLY these units!
12D. SI Base units cont. Derived units – Made up of the base units QuantitySI UnitOther UnitsAreaVolumeDensitySpeedEnergyacres, cm2, ft2m2m3L, gal, cm3mi/hr, ft/sCalorie, kWhr
13E. Unit Conversions – metric prefixes kilohectodecaunitdecicentimillikinghectorDoesn'tUsuallyDrinkChocolatemilkEXAMPLES1 000g = ________ Kg dam = _______ mm0.23 Kg =________ dg cL = ________ HL345 DaL = _____ Km Km = ___________ mm
14F. 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!
15F. Metric conversions – conversion factors Convert 34 inches to centimeters2.54cm34 in86.36 cm1inConversion factor goes here
16F. 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
17F. 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
18F. 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
19F. 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
24G. Density, cont. Units: When measuring LxWxH When measuring Volume w/ cylinder
25G. 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
26H. 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
27Watch 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.