Chapter 2
Chapter 2
Logical approach to solve problems
Observe, collect data, formulate hypothesis, test hypothesis, formulate theories supported by data
Steps may vary
Using your senses to collect information
May make measurements
May collect data
Record of facts
Logical interpretation based on knowledge and experiences
In lab, you note observations, not inferences
Inferences may be used in writing conclusions (lab reports)
Let’s test your observation skills…….
1. Are there cars parked on the sides of the road?
2. What color is the pickup truck driving on the road?
3. Are there any minivans around?4. What does the blue sign say?5. What’s the speed limit?6. Are there any pedestrians?
On the next slide, state whether the statement is an observation or an inference.
1. There is a representation of a face on one side of the coin.
2. The Latin word "Dei" means "God."3. The coin was made by deeply religious people.4. The date 1722 is printed on one side of the coin.5. The coin was made in 1722.6. The face on the coin is a representation of the
nation's president.
Do you see former President Bill Clinton and Al Gore?
Actually, it’s Clinton’s face twice with 2 different hair cuts!
Hint: There are 3 images.1. An old
lady
2. A young woman
3. A man with a big brown mustache
They are the SAME length!
A Duck, Bunny, or BOTH?
This image contains a picture and a word. Do you see both of them?
Your Your brainbrain!!
Your right brain tried to say the color,
but your left brain was reading the word.
They are all the same height!
The Landscape of Faces
How about now?
Testable statement
Basis for making predictions and for carrying out further experiments
“If-then” statements
Model◦ More than just a physical object◦ Explanation of how phenomena occur and how
data or events are related◦ Ex: atomic model of matter (atoms)
Theory◦ Broad generalization that explains facts or
phenomena
Quantitative information
Represents quantities
◦ Quantity:
Something that has magnitude, size, or amount
Not the same as a measurement
Defined in terms of standards of measurement
Have constant value, easy to preserve and reproduce, practical in size
SI Base Units
Quantity Quantity Symbol
Unit Name Unit Abbreviation
Length l meter m
Mass m kilogram kg
Time t second s
Temperature T kelvin K
Amount of substance
n mole mol
Electric current
I ampere A
Prefix Unit Abbreviation
Meaning/Example
mega M 1Mm = 1,000,000m
kilo k 1km = 1,000m
hecto h 1hm = 100m
deka da 1dam = 10m
deci d 1m = 10dm
centi c 1m = 100cm
milli m 1m = 1,000mm
micro μ 1m = 1,000,000μm
nano n 1m = 1,000,000,000nm
pico p 1m = 1,000,000,000,000pm
SI Prefixes
Derived SI UnitsQuantity Quantity
SymbolUnit Unit
AbbreviationDerivation
Area A Square meter m2 length x width
Volume V Cubic meter m3 length x width x height
Density D Kilograms per cubic meter
kg/m3 mass / volume
Molar Mass M Kilograms per mole kg/mol mass / amount of substance
Concentration
c Moles per liter M amount of substance /
volume
Molar Volume Vm Cubic meters per mole
m3/mol volume / amount of substance
Energy E joule J force x length
Measure of a quantity of matter Often confused with weight
Weight◦ measure of the gravitational pull on matter
Amount of space occupied by an object
Derived SI unit is cubic meters (m3)
The ratio of mass to volume
(Mass divided by volume)
Characteristic physical property of a substance
Does NOT depend on size of sample
Can be used as a property to identify a substance
Conversion factor- a ratio derived from the equality between two different units that can be used to convert from one unit to the other.
Accuracy◦ Closeness of measurement to the correct or
accepted value
Precision◦ Refers to the closeness of a set of measurements
of the same quantity made in the same way
100 Value
Value - Value error Percent
accepted
alexperiment accepted
Rules:1. Zeros appearing between non-zero digits are
significant.2. Zeros appearing in from of all non-zero digits
are not significant.3. Zeros at the end of a number and to the right of
a decimal point are significant.4. Zeros at the end of a number but to the left of a
decimal point may or may not be significant. If a zero has not been measured or estimated, but is
just a placeholder, it is not significant. A decimal point placed after zeros indicates that they
are significant.
When you add or subtract decimals, the answer must have the same number of digits to the right as there are in the measurement having the fewest digits to the right of the decimal.
For multiplication and division, the answer can have no more sig. figs. than are in the measurement with the fewest number of sig. figs.