Presentation on theme: "Chapter 3 Scientific Measurement"— Presentation transcript:
1 Chapter 3 Scientific Measurement Full screen view – click screen in lower right corner (Internet Explorer 4.0 & higher)
2 Section 3.1 The Importance of Measurement OBJECTIVES:Distinguish between quantitative and qualitative measurements.
3 Section 3.1 The Importance of Measurement OBJECTIVES:Convert measurements to scientific notation.
4 Measurements Qualitative measurements - words Quantitative measurements – involves numbers (quantities)Depends on reliability of instrumentDepends on care with which it is readScientific NotationCoefficient raised to power of 10
5 Working with Scientific Notation MultiplicationMultiply the coefficients, add the exponentsDivisionDivide the coefficients, subtract the denominator exponent from numerator exponent
6 Working with Scientific Notation Before adding or subtracting in scientific notation, the exponents must be the sameCalculators will take care of thisAdditionLine up decimal; add as usual the coefficients; exponent stays the same
7 Working with Scientific Notation SubtractionLine up decimal; subtract coefficients as usual; exponent remains the same
8 Section 3.2 Uncertainty in Measurements OBJECTIVES:Distinguish among the accuracy, precision, and error of a measurement.
9 Section 3.2 Uncertainty in Measurements OBJECTIVES:Identify the number of significant figures in a measurement, and in the result of a calculation.
10 Uncertainty in Measurements Need to make reliable measurements in the labAccuracy – how close a measurement is to the true valuePrecision – how close the measurements are to each other (reproducibility)Fig. 3.4, page 54
11 Uncertainty in Measurements Accepted value – correct value based on reliable referencesExperimental value – the value measured in the labError – the difference between the accepted and experimental values
12 Uncertainty in Measurements Error = accepted – experimentalCan be positive or negativePercent error = the absolute value of the error divided by the accepted value, times 100%| error |accepted value% error =x 100%
13 Significant Figures (sig. figs.) Significant figures in a measurement include all of the digits that are known, plus a last digit that is estimated.Note Fig. 3.6, page 56Rules for counting sig. figs.?Zeroes are the problemEast Coast / West Coast method
14 Counting Significant Fig. Sample 3-1, page 58RoundingDecide how many sig. figs. NeededRound, counting from the leftLess than 5? Drop it.5 or greater? Increase by 1Sample 3-2, page 59
15 Sig. fig. calculations Addition and Subtraction The answer should be rounded to the same number of decimal places as the least number in the problemSample 3-3, page 60
16 Sig. Fig. calculations Multiplication and Division Round the answer to the same number of significant figures as the least number in the measurementSample 3-4, page 61
17 Section 3.3 International System of Units OBJECTIVES:List SI units of measurement and common prefixes.
18 Section 3.3 International System of Units OBJECTIVES:Distinguish between the mass and weight of an object.
19 International System of Units The number is only part of the answer; it also need UNITSDepends upon units that serve as a reference standardThe standards of measurement used in science are those of the Metric System
20 International System of Units Metric system is now revised as the International System of Units (SI), as of 1960Simplicity and based on 10 or multiples of 107 base unitsTable 3.1, page 63
21 International System of Units Sometimes, non-SI units are usedLiter, Celsius, calorieSome are derived unitsMade by joining other unitsSpeed (miles/hour)Density (grams/mL)
22 Length In SI, the basic unit of length is the meter (m) Length is the distance between two objects – measured with rulerWe make use of prefixes for units larger or smallerTable 3.2, page 64
26 Volume changes?Volume of any solid, liquid, or gas will change with temperatureMuch more prominent for GASESTherefore, measuring instruments are calibrated for a specific temperature, usually 20 oC, which is about normal room temperature
27 Units of Mass Mass is a measure of the quantity of matter Weight is a force that measures the pull by gravity- it changes with locationMass is constant, regardless of location
28 Working with MassThe SI unit of mass is the kilogram (kg), even though a more convenient unit is the gramMeasuring instrument is the balance scale
29 Section 3.4 Density OBJECTIVES: Calculate the density of an object from experimental data.
30 Section 3.4 Density OBJECTIVES: List some useful application of the measurement of specific gravity.
31 Density Which is heavier- lead or feathers? It depends upon the amount of the materialA truckload of feathers is heavier than a small pellet of leadThe relationship here is between mass and volume- called Density
32 Density The formula for density is: mass volume Common units are g/mL, or possibly g/cm3, (or g/L for gas)Density is a physical property, and does not depend upon sample sizeDensity =
33 Things related to density Note Table 3.7, page 69 for the density of corn oil and waterWhat happens when corn oil and water are mixed?Why?Will lead float?
34 Density and Temperature What happens to density as the temperature increases?Mass remains the sameMost substances increase in volume as temperature increasesThus, density generally decreases as the temperature increases
35 Density and water Sample 3-5, page 71 Water is an important exception Over certain temperatures, the volume of water increases as the temperature decreasesDoes ice float in liquid water?Why?Sample 3-5, page 71
36 Specific GravityA comparison of the density of an object to a reference standard (which is usually water) at the same temperatureWater density at 4 oC = 1 g/cm3
37 Formula Note there are no units left, since they cancel each other D of substance (g/cm3)D of water (g/cm3)Note there are no units left, since they cancel each otherMeasured with a hydrometer – p.72Uses? Tests urine, antifreeze, batterySpecific gravity =
38 Section 3.5 Temperature OBJECTIVES: Convert between the Celsius and Kelvin temperature scales.
39 Temperature Heat moves from warmer object to the cooler object Glass of iced tea gets colder?Remember that most substances expand with a temp. increase?Basis for thermometers
40 Temperature scales Celsius scale- named after a Swedish astronomer Uses the freezing point(0 oC) and boiling point (100 oC) of water as referencesDivided into 100 equal intervals, or degrees Celsius
41 Temperature scales Kelvin scale (or absolute scale) Named after Lord KelvinK = oC + 273A change of one degree Kelvin is the same as a change of one degree CelsiusNo degree sign is used
42 Temperature scales Water freezes at 273 K Water boils at 373 K 0 K is called absolute zero, and equals –273 oCFig. 3.19, page 75Sample 3-6, page 75