Chapter 2 Measurements and Calculations -...
Transcript of Chapter 2 Measurements and Calculations -...
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Chapter 2
Measurements and Calculations
2.1 Scientific Method
◦ Observe/Collect Data
◦ Hypothesis
◦ Test/Experiment
◦ Theorize
System
◦ Specific matter in a given space that is selected to be studied.
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2.2 Units of Measurement
Qualitative
◦ Given results in a descriptive non-numerical form.
◦ General observations describing the object.
Quantitative
◦ Given results in a definite form, usually numerical.
◦ Precise observation using number values.
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SI measurement
International System of Units (S.I.)
◦ Le Systeme International d`Unites.
◦ Table 1 lists all base units page 34
Mass vs. Weight
◦ Mass – kilogram (kg), measures the amount of
matter.
◦ Weight – is the force of gravity on a sample of
matter.
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Derived Units
Combination of two or more SI base units.
◦ Volume = amount of space occupied by an object.
length x width x height = (m3)
Liquid Volume – (mL)
◦ Density = ratio of mass to volume.
V
mD
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Conversion Factors
Ratio derived from the equality between two
different units, that can be used to convert from
one to the other.
◦ 1 dollar = 4 quarters
dollar 1
quarters 4or
quarters 4
1dollar
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Dimensional Analysis
Mathematical technique to help solve
problems using conversion factors.
dollars 11.25
quarters 4
1dollar
1
quarters 45x
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Metric System
The International System of Units
Standard
Based upon tens or decimal places.
Used throughout the world.
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Table of Prefixes Prefix Abbrev. Meaning
Tera- T 1012
Giga- G 109
Mega- M 106
kilo- k 103
hecto- h 102
deca- da 101
Base Units - meter, liter, gram, or second
deci- d 10-1
centi- c 10-2
milli- m 10-3
micro- µ 10-6
nano- n 10-9
pico- p 10-12
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Metric Conversions
Convert 50 kg to g.
Convert 30 cm to m.
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Metric Conversions
Identify the conversion factors needed to
convert cm to mm.
Identify the conversion factors needed to
convert cm3 to mm3.
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Conversion of Cubic Units of
Volume Practice
◦ 1) 1.2 x 10-3 nm3 = ? mL
◦ 2) 1.4 x 10-2 m3 = ? mm3
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2.3 Using Scientific Measurements
Accuracy
◦ How close a single measurement comes to the
actual dimension or true value.
Precision
◦ How close several measurements are to the
same value.
Page 44 – Dart board illustration
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Percentage Error
accepted
acceptedexperiment
Value
Value Value error %
Error in Measurement
Measurements always contain some
degree of error.
+/- .5 error
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Significant Figures
In a measurement include all the digits that
are known precisely plus one last digit that
is estimated.
Page 47 - Rules for Significant Figures
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Significant Figures
Rules for significant digits: ◦ All non-zero digits are significant.
1234 5663 121112
◦ Zeroes in between two non-zero digits are always significant. 103 1004 102003
◦ Zeroes after a non-zero digits are only significant if the number has a decimal. 200. 3450. 10.
◦ Zeroes after non-zero digits are not significant if the number has no decimal. 200 40020 4230
◦ Zeroes in front of non-zero digits are never significant. .00004 0.0343 .00430
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Sig Figs in Calculations
An answer can’t be more precise than the
least precise measurement from which it
was calculated.
Multiplication & Division
◦ Round all answers to the fewest sig fig.
Addition & Subtraction
◦ Round to the same number of decimal places as
the measurement with the least precision.
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Sample Problems
1) (5.232x106 mm )(4.33x102mm)=
2)
3) 4.33x102cm + 1.2x102cm=
4) 7.90 kg – 4.2 kg=
L 8.2x10
g5.44x104
7
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Scientific Notation
Scientific Notation or Exponential
Notation
◦ Written as the product of two numbers.
Coefficient and a power of 10.
◦ n. x 10e
◦ Where n is a digit 1-9. e is the exponent.
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Proportions
Directly Proportional
◦ Dividing one quantity by the other gives a
constant value.
Inversely Proportional
◦ Product of two quantities are constant values.
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Density
Density is the mass per unit of volume.
D = m/v
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Density Lab
Line of best fit.
Excel graph for each metal.
Excel Graph example