Thursday, October 31, 2013



Happy Halloween!
Standard IE1: Scientific
progress is made by
asking meaningful
questions and
conducting careful
scientific experiments.
Independent Practice:


Section 3.3 Reading
Packet
Question: Copy the
chart into your Journal.
Quantity
SI Base
Unit
Symbol
Length
Meter
m
Mass
Kilogram
kg
Temp
Kelvin
K
Time
Second
s
Amount of
Substance
Mole
mol
Luminous
Intensity
Candela
cd
Electric
Current
Ampere
A
Measurements
and
Calculations
Units of Measurement
 Measurements
involve NUMBER and UNIT
 Represent a quantity: has magnitude, size,
or amount
 Gram = unit of measurement
 Mass = quantity
Units of Measurement
 Scientists
system…



around the world agree on one
International System of Units (le Systeme
International d’Unites)
SI units
Built from seven base units
SI Base Units
Units of Measurement
Units of Measurement
 Metric
Prefixes – make units easier to use
 Make the unit smaller or larger
 Unit = prefix + base unit
 Table pg. 74
Mass
 Measures
quantity of matter
 SI unit: kilogram, kg
 ______ kg = _____ g
 gram used for smaller masses
 Weight: measure of gravitational pull
Length
 SI
unit: meter, m
 Longer distances: kilometer, km
 _______ km = _______ m
 Shorter distances: centimeter, cm
 _______ m = ________ cm
Volume
 SI
unit: m3
 A derived unit: combination of base units by
multiplying or dividing
 SI unit for Area: l x w = m x m = m2
 Volume: l x w x h = m x m x m = m3
 Also: liters (L), mL, dm3 and cm3
 1 L = 1 dm3 = 1000mL = 1000 cm3
Derived Units
Scientific Notation
 Put
the numbers in the form
a x 10n
 a has one # to left of decimal
 If # is bigger than 1  + exponent
 If # is less than 1  - exponent
Scientific Notation
 Review:
Write in scientific notation or
standard notation.
a. 32,700
b. 0.0003412
c. 3.901 x 10-6
d. 4.755 x 108
Let’s Practice
Scientific Notation
Worksheet
Significant Figures (Sig Figs)
 How
many numbers mean anything?
 When we measure, we can (and do) always
estimate between the smallest marks.
1
2
3
4
5
Significant Figures (Sig Figs)
 Better
marks better estimate.
 Last number measured actually an
estimate
1
2
3
4
5
Rules for Significant Figures
1)
All nonzero digits are significant.
•
457 cm has 3 sig figs
•
2.5 g has 2 sig figs
2)
Zeros between nonzero digits are significant.
•
1007 kg has 4 sig figs
•
1.033 g has 4 sig figs
3)
Zeros to the left of the first nonzero digit are not significant. They are not actually
measured, but are place holders.
•
0.0022 g has 2 sig figs
•
0.0000022 kg has 2 sig fig
4)
Zeros at the end of a number and to the right of a decimal are significant. They are
assumed to be measured numbers.
•
0.002200 g has 4 sig figs
•
0.20 has 2 sig figs
•
7.000 has 4 sig figs
5)
When a number ends in zero but contains no decimal place, the zeros may or may
not be significant. We use scientific (aka exponential) notation to specify.
•
7000 kg may have 1, 2, 3 or 4 sig figs!
Sig Figs
 What
is the smallest mark on the ruler that
measures 142.15 cm?
 142 cm?
 140 cm?
 Does the zero mean anything? (Is it significant?)
 They needed a set of rules to decide which
zeroes count.
Sig Figs.
 405.0
g
 4050 g
 0.450 g
 4050.05 g
 0.0500060 g
Sig Figs
 Only
measurements have sig figs.
 Counted numbers are exact – infinite sig
figs
 A dozen is exactly 12
 Conversion factors: 100 cm = 1 m
Problems
 50
has only 1 significant figure
 if it really has two, how can I write it?
 Scientific notation
x 101
2 sig figs
 Scientific Notation shows ALL sig figs
 5.0
Rounding Rules
 Round



454.62 to four sig figs
to three sig figs
to two sig figs
to one sig fig
Sig Figs
 How
many sig figs in the following
measurements?
 458 g
 4085 g
 4850 g
 0.0485 g
 0.004085 g
 40.004085 g
Let’s Practice
Significant Figures
Worksheet
Calculations
1.
2.
3.
165.86 g + 4.091g - 140 g + 27.32 g
(35.6 L + 2.4 L) / 4.083 =
2.524 x (16.408 m – 3.88 m) =
Answers: 57g
9.31 L 31.62 m
Let’s Practice
Significant Figures in
Calculations WS
Density
 Density
= mass
D=m
volume
V
 Units: g/cm3 or g/mL but SI unit is kg/m3
 derived unit
 Used to identify substances
 Varies with temperature
 As temp. increases density…
Density
Density Examples
 If
a metal block has a mass of 65.0 grams
and a volume of 22 cubic centimeters,
what is the density of the block?
D=m
V
 D = 65.0 g = 3.0 g/cm3
22 cm3
Density Examples
 Aluminum
has a density of 2.7 g/cm3.
What volume of aluminum has a mass of
60 grams?
D=M
V
20 cm3
Density Examples
 Gold
has a density of 19.3 g/cm3. A block
of metal has a mass of 80 g and a volume
of 12 cm3. Could this block be a piece of
gold?
 No, because this block has a density of 7
g/cm3s
Unit Conversions
Unit Conversions

1.
2.
3.
Given information in one unit  need to
find the equivalent in another unit
Identify what’s given
Organize plan of attack
Carry out plan WITH UNITS!!
Conversion factors
ratio of equivalent measurements.”
 Start with two things that are the same.
1 m = 100 cm
 Can divide by each side to come up with
two ways of writing the number 1.
 “A
Conversion factors
1m
100 cm
=
100 cm
100 cm
Conversion factors
1m
100 cm
=
1
Conversion factors
1m
100 cm
1m
1m
=
=
1
100 cm
1m
Conversion factors
1m
100 cm
1
=
=
1
100 cm
1m
Conversion Factors
 Unique
way of writing the number 1.
 Does NOT change the VALUE, it changes
the UNITS.
Write the conversion factors
for the following
 kilograms
to grams
 feet to inches
 1 L = 1 dm3 = 1000mL = 1000 cm3
Let’s See How They Work
 We
can multiply by a conversion factor
creatively to change the units .
 13 inches is how many yards?
Let’s Try Some!
 323
mm = _____ nm
 3.2 miles = _____ in
 250 gallons = _____ mL
 15 days = _______ min
More Unit Conversions
More Involved
Derived Unit Conversions
 54.3
cm3 = ______ m3
 7.54
ft2 = _______ in2
Derived Unit Conversions
 125.3
m/s = ______ mi/hr
 625
g/mL = ______ kg/m3
 100
km/hr = ______ mi/hr
Let’s Practice
Dimensional Analysis
Where do these measurements come
from?
Recording Measurements
Making Good Measurements

1.
We can do 2 things:
Repeat measurement many times
- reliable measurements get the same number
over and over
- this is PRECISE
Making Good Measurements
2. Test our measurement against a
“standard”, or accepted value
- measurement close to accepted value is
ACCURATE
Video - 46
Measurements are Uncertain
1.
2.
3.
4.
Measuring instruments are never perfect
Skill of measurer
Measuring conditions
Measuring always involves estimation


Flickering # on balance
Between marks on instrument
Estimating Measurements
Error
 Probably
not EXACTLY 6.35 cm
 Within .01 cm of actual value.
 6.35 cm ± .01 cm
 6.34 cm to 6.36 cm
Calculating Percent Error
 Compares
your measurement to accepted
Valueexperimental -Valueaccepted
value
Percentage error =
× 100
Valueaccepted
 Negative
if measurement is small
 Positive if measurement is big
Calculating Percent Error
 What
is the % error for a mass
measurement of 17.7g, given that the
correct value is 21.2g?
Let’s Practice
Percent Error Worksheet