chapter 2 analyzing data. si measurement si (def): le systeme international d’ unites...
TRANSCRIPT
CHAPTER 2
ANALYZING DATA
SI MEASUREMENT
SI (def): Le Systeme International d’ Unites (International System of Units)
SI has 7 base units and almost all other units are derived from these.
SI MEASUREMENT
QUANTITY QUANTITY SYMBOL
UNIT NAME
UNIT ABBREVIATION
Length l meter m (not italicized)
Mass m(italicized)
kilogram kg
Time t second s
Temperature T Kelvin K
SI MEASUREMENT
QUANTITY QUANTITY SYMBOL
UNIT NAME
UNIT ABBREVIATION
Amount of substance
n mole mol
Electric current
I ampere A
Luminous intensity
IV candela cd
SI MEASUREMENT
Prefixes are added to the base units to represent larger or smaller quantities.
Table 2.2: SI Prefixes, pg. 33
MUST MEMORIZE
SI MEASUREMENT
SI MEASUREMENT
SI units are defined in terms of standards of measurement. They are either objects or consistent natural phenomena.
International organizations monitor the defining process. In the US, the National Institute of Standards and Technology plays a major role in setting standards
DERIVED UNITS
1) Derived SI units: combinations of SI base units
Examples:
density = mass
volume
DERIVED UNITS
2) volume: amount of space occupied by an object
non-SI volume unit:
liter, L 1 L = 1000 cm3
SI volume unit: m3
DERIVED UNITS 3) density: mass per unit volume
d = m/V
Mass and volume change proportionately, meaning that the ratio of m to V is constant. Density is an intensive property.
Density and temperature: at high T, most objects expand.
SCIENTIFIC NOTATION
Scientific Notation: numbers written in the form M x 10n, where the factor M is a number greater than or equal to 1 but less than 10, and n is a whole number.
65 000 km 6.5 x 104 km
0.0012 mm 1.2 x 10-3 mm
Scientific Notation Rules
To find M: Move the decimal point in the original # to the left or right so that only one nonzero digit remains to the left of the decimal point
To find n: Count the # of places that you moved the decimal point
(Moved left, n = + Moved right, n = - )
SCIENTIFIC NOTATION
Addition and Subtraction: Values must have same value exponent before you can do these operations
Multiplication: M factors are multiplied and exponents are added
Division: M factors divided and exponent of denominator subtracted from exponent of numerator
3
3
cm
gcm
Dimensional Analysis
The “Factor-Label” Method Units, or “labels” are canceled, or
“factored” out
g
Dimensional Analysis
Steps:
1. Identify starting & ending units.
2. Line up conversion factors so units cancel.
3. Multiply all top numbers & divide by each bottom number.
4. Check units & answer.
Dimensional Analysis
Lining up conversion factors:
1 in = 2.54 cm
2.54 cm 2.54 cm
1 in = 2.54 cm
1 in 1 in
= 1
1 =
Dimensional Analysis
How many milliliters are in 1.00 quart of milk?
1.00 qt 1 L
1.057 qt= 946 mL
qt mL
1000 mL
1 L
Dimensional Analysis
You have 1.5 pounds of gold. Find its volume in cm3 if the density of gold is 19.3 g/cm3.
lb cm3
1.5 lb 1 kg
2.2 lb= 35 cm3
1000 g
1 kg
1 cm3
19.3 g
Dimensional Analysis
How many liters of water would fill a container that measures 75.0 in3?
75.0 in3 (2.54 cm)3
(1 in)3= 1.23 L
in3 L
1 L
1000 cm3
Dimensional Analysis
5) Your European hairdresser wants to cut your hair 8.0 cm shorter. How many inches will he be cutting off?
8.0 cm 1 in
2.54 cm= 3.2 in
cm in
Dimensional Analysis
6) Taft football needs 550 cm for a 1st down. How many yards is this?
550 cm 1 in
2.54 cm= 6.0 yd
cm yd
1 ft
12 in
1 yd
3 ft
Dimensional Analysis
7) A piece of wire is 1.3 m long. How many 1.5-cm pieces can be cut from this wire?
1.3 m 100 cm
1 m= 86 pieces
cm pieces
1 piece
1.5 cm
A. Accuracy vs. Precision
Accuracy - how close a measurement is to the accepted value
Precision - how close a series of measurements are to each other
ACCURATE = CORRECT
PRECISE = CONSISTENT
ERROR
B. Percent Error
Indicates accuracy of a measurement
100literature
literaturealexperimenterror %
your value
accepted value
% Error Problems
Try the two practice problems on the outline.
Percent Error Examples
a. What is the % error for a mass measurement of 17.7 g if the correct value is 21.2 g?
17.7 g – 21.2 g x 100 =
21.2 g
b. A volume is measured experimentally to be 4.26 mL. What is the % error if the correct value is 4.15 mL?
4.26 mL – 4.15 mL x 100 =
4.15 mL
ERROR IN MEASUREMENT
In any measurement, some error or uncertainty exists
Measuring instruments themselves place limitations in precision
Estimate the final questionable digit.
D. Significant Figures
Indicate precision of a measurement.
Recording Sig Figs– Sig figs in a measurement include the known
digits plus a final estimated digit
2.35 cm
SIGNIFICANT FIGURES
Significant ≠ Certain
Must memorize the rules for recognizing significant figures!
SIG. FIGS. RULESRULE EXAMPLE
1. No zeros, All sig. 852 m 97.25 mL
2. Zeros between nonzero digits = sig.
40.7 L 87009 km
3. Zeros at front of nonzero digits ≠ sig.
0.095897 m0.0009 kg
4. Zeros at end of # and to right of decimal = sig.
85.00 g9.000 000 000 mm
5. Decimal after zeros, sig. Zeros with no decimal ≠ sig
2000 m2000. m
Atlantic-Pacific Check
Pacific, Atlantic,
Decimal is Decimal is
Present Absent
Significant figures practice
Try the practice problems on the outline
Sig. Figs. Practice
a) 804.05 g
b) 0.0144030 km
c) 1002 m
d) 400 mL
e) 30000. cm
f) 0.000625000 kg
ROUNDING RULES
Digit after last digit to be kept:
Last digit should: Examples (3 sig. Figs)
> 5 Increase by 1 42.68 g 42.7 g
< 5 Stay the same 17.32 m 17.3 m
5, followed by nonzero
Increase by 1 2.7851 cm 2.79 cm
5, preceded by odd
Increase by 1 4.635 kg 4.64 kg
5, preceded by even
Stay the same 78.65 mL 78.6 mL
C. Significant Figures
Calculating with Sig Figs (con’t)– Add/Subtract - The # with the lowest decimal
value determines the place of the last sig fig in the answer.
3.75 mL
+ 4.1 mL
7.85 mL 7.8 mL
3.75 mL
+ 4.1 mL
7.85 mL
C. Significant Figures
Calculating with Sig Figs– Multiply/Divide - The # with the fewest sig figs
determines the # of sig figs in the answer.
(13.91g/cm3)(23.3cm3) = 324.103g
324 g
4 SF 3 SF3 SF
Sig. Figs./Rounding Practice
Try the practice problems on the outline.
Practice Problems
1. What is the sum of 2.099 and 0.05681?
2. Calculate the quantity 87.3 cm – 1.655 cm
3. Polycarbonate has a density of 1.2 g/cm3. A photo frame is constructed from two 3.0 mm sheets. Each side measures 28 cm by 22 cm. What is the mass of the frame?
Conversion Factors
Conversion factors are typically exact.
Do not count when determining # of significant figures in answer.
E. Proportions
Direct Proportion
Inverse Proportion
xy
xy
1
y
x
y
x
Direct and Indirect Proportions
Direct: 2 quantities are directly proportional if dividing one by the other gives a constant value; graph is a straight line, y/x = k
Indirect: 2 quantities are indirectly proportional if their product is constant, graph curved, xy = k or y α 1/x
GRAPHS