Transcript 5.2 x 10 4

Chapter 1. Section 2: The Way Science Works
Critical thinking helps you solve problems logically.
Scientists use scientific methods to
solve problems.
• The scientific method involves critical thinking
in that it entails thinking about a problem and
making objective judgments about the results.
Laws & Theories
• In science, a law is a summary of many
experiments, results and observations.
• A law only describes what happens, not why it
happens.
• A law also predicts the results of experiments
not done yet.
• An explanation of why things work the way
they do is called a theory.
• A theory explains the results of many kinds of
experiments and observations.
• Theories are always open to challenges and
testing.
Remember:
• A hypothesis is an educated guess based on
accurate and relevant information.
• A law is a summary of experimental results
and observations and tells us what will
happen (but doesn’t explain why).
• A theory is an explanation that can be used to
predict what will happen in new situations.
Units of Measurement
Scientists use standard units of measure that
together form the International System of
Units, or SI. SI stands for the French term le
Système Internationale d’Unités.
SI Units
• SI units give consistency.
SI Units
Unit
Symbol
Quantity
Meter
m
Length
Kilogram
kg
Mass
Second
s
Time
Ampere
A
Electric current
Mole
mol
Amount of
substance
Candela
cd
Luminous intensity
Kelvin
K
Temperature
Derived units: Area, Volume, Density
Metric Units
King Henry Died ____ Drinking Chocolate Milk
Kilo hecto deca ____ deci centi milli
1000 100
10
Base
10
100
1000
Metric Conversions
1.85 m = ______ cm
7 m = _______ cm
1.6 kg = ______ g
2800 mg = _____ g
Bellwork 8/20/14
• How many miles will a person run during a 10K
race? (1 km = .621 miles)
• A family pool holds 10,000 gallons of water. How
many m3 is this? (264.2 gal = 1 m3)
• How many seconds are in 1 year? …hmmm
• Pepsi puts 355 ml of soda in a can. How many
drops is this? (20 drops = 1mL)
Derived Units
• Area, in m2, is the size of a 2-dimensional
surface
• Volume is the amount of space a substance
occupies
Units in m3 or cm3 or liters (L).
Density
m
d
V
g/cm3
g/mL
1. A sample of aluminum has a volume of 15.0 mL
and weighs 40.5 g. What is its density?
2. Calculate the density of sulfuric acid if 35.4 mL
of the acid weighs 65.14 g.
3. What is the density of CO gas if 0.196 g occupies
a volume of 100 ml?
4. A block of wood 6 cm on each side has a
mass of 217 g. What is the density of the
block? (Hint, don’t forget to find the
volume of the wood.)
5. 100 grams of a liquid completely fill a 200
mL bottle. What is the density of the
liquid?
6. A solution has a density of 1.50 g/mL.
How many grams are needed to obtain 10.0
mL of solution?
7. What is the mass of the ethyl alcohol that
exactly fills a 200.0 mL container? The density
of ethyl alcohol is 0.789 g/mL.
8. If a 96.5g piece of aluminum has a density of
2.7 g/cm3, what is its volume?
9. 100 grams of a liquid completely fill a 200 mL
bottle. What is the density of the liquid?
9. Chloroform is a liquid with a sticky sweet odor
that was once used as a surgical anesthetic. If
the density of chloroform is 1.49 g/cm3, what
is the volume of 25 g of chloroform?
10. If a 96.5g piece of aluminum has a density of
2.7 g/cm3, what is its volume?
Section 3: Organizing Data
• Key Ideas
Why is organizing data an important science
skill?
How do scientists handle very large and very
small numbers?
How can you tell the precision of a
measurement?
Charts & Graphs
Scientific Notation
• t = distance from Earth to Neptune (m)
speed of light (m/s)
t = 4,500,000,000,000 m
300,000,000 m/s
t = 4.5 1012 m
3.0 x 108 m/s
OR…
When should you use scientific
notation?
• To express really large or really small numbers
103
1000
102
100
101
10
100
1
10-1
0.1
10-2
0.01
10-3
0.001
Scientific Notation
602 200 000 000 000 000 000 000 atoms
5280 = 5.28 x 103
0.0821 = 8.21 x 10 -2
Scientific Notation
0.00235 m
46000 cows
112 pm
0.760 µg
Use scientific notation to make
calculations.
(2.3 x 105) x (5.2 x 104) =
(2.3 x 10-5) x (5.2 x 10-4) =
(2.3 x 105) =
(5.2 x 104)
(5.2 x 104) =
(2.3 x 10-5)
Use Scientific Notation to make
calculations
• The adult human heart pumps about 18,000 L
of blood each day. Write this value in
scientific notation.
• Your county plans to buy a rectangular tract of
land measuring 5.36 x 103 m by 1.38 x 104 m
to establish a nature preserve. What is the
area of this tract?
Accuracy vs. Precision
Accuracy & Precision
• Accuracy is a description of how close a
measurement is to the actual/true value.
– This was hitting the basket! Or hitting a bullseye.
• Precision is the exactness of a
measurement(repeatable).
– This was hitting in the same place more than
once.
Precision in Measurements
• Scientists use significant figures to show the
precision of a measured quantity.
• They are the uncertain part of the
measurement.
• Significant figures tell you how precise a
measurement is.
cm
cm
Significant Figures
• Scientists use significant figures to show the
estimated part of measurements.
• The number of figures tells us the precision of
the measurement.
• 4.13
• .5347
612.78
.9567
• Remember this rule: The number of sig figs is
the number of sig figs in the least precise
measurement.
Significant Figures Practice Time!
Round the following to the number of sig figs in
the parentheses:
7.376 (2 sig figs)
362.306 (5 sig figs)
0.5234 (2 sig figs)
.2395 (3 sig figs)
Here are more!
• Write the answers in the correct number of sig
figs.
• 15.75 m x 8.45 m =
• 5,650 L ÷ 27 min =
(3)
(2)
• Calculate the volume of a room that is 3.125
m high, 4.23 m wide and 5.75 m long. Write
the answer with the correct number of sig
figs.
• Find the area of a rectangle that is 8.5 cm long
and 3.45 cm wide. Round your answer to the
correct number of significant figures.