chapter 2 – measurements & calculations. table of contents sectiontitle 1 scientific method 2...
TRANSCRIPT
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Chapter 2 – Measurements & Calculations
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Table of Contents
Section Title1 Scientific Method
2 Units of Measure
3 Using Scientific Measurements
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Objectives (Section 1)
Describe the purpose of the scientific method.
Distinguish between qualitative and quantitative observations.
Describe the differences between hypotheses, theories, and models.
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The Scientific Method
Science progresses through carefully planned investigation
Scientific Method is a logical approach to solving problems by observing and collecting data, formulating hypotheses, testing hypotheses, and formulating theories that are supported by data.
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Which chemical is the best penny cleaner?
Which is a better penny cleaner?
1. Ketchup
2. Vinegar
3. Salt
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Observing & Collecting Data
• Observing is the use of the senses to obtain information.
• data may be • qualitative (descriptive)• quantitative (numerical)
• A system is a specific portion of matter in a given region of space that has been selected for study during an experiment or observation.
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Qualitative vs. Quantitative Data
Which is a better penny cleaner?
What is the length of this pen?
Which is more subjective? Why?
Which is considered more desirable for science? Why?
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Formulating Hypotheses
• Scientists make generalizations based on the data.
• Scientists use generalizations about the data to formulate a hypothesis, or testable statement.
Hypotheses are often “if-then” statements.
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Testing Hypotheses
• Testing a hypothesis requires experimentation that provides data to support or refute a hypothesis or theory.
• Controls - experimental conditions that stay constant
• Variables - experimental conditions that change
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Theorizing
• A model in science is more than a physical object; it is often an explanation of how phenomena occur and how data or events are related.• visual, verbal, or mathematical• example: atomic model of matter
• A theory is a broad generalization that explains a body of facts or phenomena. example: atomic theory
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Scientific Method (Visually)
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Algebra Review
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Scientific Notation Pages
Converting to Scientific Notation Move decimal to have one digit (non-zero) to the LEFT
Example: 234 = 2.34 x 102
Example 2: 0.52 = 5.2 x 10-1
Decimal to the RIGHT = Negative exponent
Decimal to the LEFT = Positive exponent
Complete pp. 2 #1-5
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Scientific Notation Pages (2)
Converting from Scientific Notation Move decimal to a regular value
Example: 4.92 x 102 = 492
Example 2: 5.2 x 10-4 = 0.00052
Positive exponent = MOVE decimal to the RIGHT
Negative exponent = MOVE decimal to the LEFTNegative exponents = SMALLER than 1
Complete pp. 2 #1-5
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Exponent Operations
Use the calculator!!
Don’t forget the parentheses
Complete pp. 3 #1, 3, 5, & 7
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Significant Figures & Operations
Use the rules on page 4 + pp. 47 !!
For add/subtract OR multiply/divide, use the rules on page 5 + pp. 49 !!
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Significant Figures
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Significant Figs & Operations
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Section 2.2 – Units of Measurement
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Lesson Starter
Would you be breaking the speed limit in a 40 mi/hr zone if you were traveling at 60 km/hr?
one kilometer = 0.62 miles
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Lesson Starter
Would you be breaking the speed limit in a 40 mi/hr zone if you were traveling at 60 km/hr?
one kilometer = 0.62 miles
60 km/h = 37.2 mi/h
You would not be speeding!
km/h and mi/h measure the same quantity using different units
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Objectives 2.2
Distinguish between a quantity, a unit, and a measurement standard.
Name and use SI units for length, mass, time, volume, and density.
Distinguish between mass and weight.
Perform density calculations.
Transform a statement of equality into conversion factor.
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Measurement vs. Quantity
Measurements represent quantities.
A quantity is something that has magnitude, size, or amount.
measurement quantity the teaspoon is a unit of measurement volume is a quantity Measurement = number + unit
The choice of unit depends on the quantity being measured.
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SI Measurement
Scientists all over the world have agreed on a single measurement system called Le Système International d’Unités, abbreviated SI.
SI has 7 base units Everything else is DERIVED from these 7 units Hence, called Derived SI unit
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SI Base Units
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7 Base Units
L-MM-TT (Length, Mass, Mole, Time, Temp)
Current (A)
Luminous Intensity (cd)
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Prefix Symbol 10n Common
Kilo k 103 Thousand
hecto h 102 Hundred
deca da 101 Ten
100 One or Unit
deci d 10-1 Tenths
centi c 10-2 Hundredth
milli m 10-3 Thousandth
SI Prefixes – Need to Know
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SI Prefixes - Extended
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Converting SI Units
Kilo hecto deca U deci centi milli
Complete pages 6 & 7
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Mass vs. Weight
Mass is a measure of the quantity of matter.Kilogram (kg)
Weight is a measure of the gravitational pull on matter.Newtons (Don’t need to know units now)
Mass does not depend on gravity.
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Length Matters
Length is a measure of distance.Meter (m)
Kilometer (km) – longer distances
Centimeter (cm) – shorter distances
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Derived SI Units
Combine more than one SI unit into a new unit
Called derived SI units since they are derived from the 7 SI units
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Volume
Volume is the amount of space occupied by an object.
Cubic meters (m3) Cubic centimeter (cm3) is often used Liter (L) is a non-SI unit 1 L = 1000 cm3
1 mL = 1 cm3
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Density
Density is the ratio of mass to volume, or mass divided by volume.
kg / m3
Can also use: g/mL = g/cm3
density =
mass
volume or D =
m
V
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Conversion Factor
Conversion factor is a ratio derived from the equality between two different units that can be used to convert from one unit to the other.
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Accuracy & Precision
Accuracy refers to the closeness of measurements to the correct or accepted value of the quantity measured.
Precision refers to the closeness of a set of measurements of the same quantity made in the same way.
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Accuracy & Precision
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Percentage Error
Percentage error is calculated by subtracting the accepted value from the experimental value, dividing the difference by the accepted value, and then multiplying by 100.
Percentage error = Value
experimental-Value
accepted
Valueaccepted
× 100
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Percentage Error Problems
A student measures the mass and volume of a substance and calculates its density as 1.40 g/mL. The correct, or accepted, value of the density is 1.30 g/mL. What is the percentage error of the student’s measurement?
What is the percentage error for a mass measurement of 17.7g, given the correct value is 21.2g?
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Percentage Error Problems
€
1.4 −1.3
1.3×100 = 7.7%
€
17.7 −21.2
21.2×100 = 17%
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Section Review & HW
Complete Section Review pp. 42 & pp. 57
Complete Practice Problems pp. 59 (#16 – 23)