Transcript Ch 01 Overpopulation Chart

Chapter 2
Milbank High School
The Science of Physics
Measurements
Vocabulary
Ammann
Matter, Energy, & Ideas
Matter: Something that occupies space and has mass
Energy: The ability to do work.
Law of Conservation of Energy and Matter:
Energy and Matter are neither created nor
destroyed but only changed in form.
Matter and Energy are interchangeable:
E = mc2
Hypothesis-- Scientific Guess.
Theory-- An idea with much supporting evidence.
Law or Principle-- It's proved. No exceptions.
Observations
Subjective observation (qualitative)-- depends
upon opinion.
Examples:
It's hot in here.
He’s a Shorty.
Optical Illusions fool the eye.
Objective observation (quantitative)-- is measured.
It is factual.
Examples:
It's 22oC in here.
He’s 1.7 meters tall.
He's 94 cm around.
Measurement
Since the formal practice of
Science began, Scientists have
needed a definite way to both
record and share their findings
with the world
Early measurements troubled by
inconsistencies
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Cubits, fathoms, the foot were all used to
measure lengths
Scientists from around the world agreed
that a single set of units were needed
The System International (SI) was formed
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Based on the metric system
Fundamental Units of the SI
system
You need to use UNITS!
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Without units numbers are meaningless,
from this point any numbers should be
appropriately “dressed” with the proper
units.
We will use the “MKS“ System
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Meter, Kilogram, Seconds
Do not use the “CGS” System
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Centimeter, Gram, Seconds
Mass
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The measure of how much material an
object is made of.
It is also a measure of the inertia, the
resistance force to a change on motion.
Mass is often confused with weight, the
force of attraction with the earth.
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An object in space has the same mass, but
changes to zero weight units!
Objects in the MKS system
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Telephone
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Length of hand set cord : 1 meter
Mass
: 1 Kilogram
Duration of one ring
: 1 second
Car
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Length of the Car
: 5 meters
Mass
: 1000 KG
Duration of 0 to 60 MPH: 6.2 second
Common English to Metric
conversions
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1 centimeter = 0.394 inches
1 inch = 2.54 centimeters
1.0 slug)g = weight (mixed mass units)
(1.0 slug) (32.174 ft/s2) = 32.174 pounds
I.e., 1.0 slug (mass) is equivalent to
32.174 pounds (weight
1 pound (lb) = .45 kg
1 kg = 2.2 pounds (lb)
Summary
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The meter, second, and kilograms are SI base
units of length, time, and mass
Fundamental units can be combined
mathematically to form DERIVED units.
Prefixes are used to change SI units by powers
of 10
The international system of units (SI) allows
scientists and engineers to exchange data
MKS units use kilograms instead of grams and
meters instead of centimeters, both CGS and
MKS use seconds for time units
Metric Prefixes
Significant Digits
What are they?
And
How do you use them?
Accuracy:
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This is the concept which deals with whether a
measurement is correct when compared to the known
value or standard for that particular measurement.
When a statement about accuracy is made, it often
involves a statement about percent error.
Percent error is often expressed by the following
equation:
% error = (|experiment value - accepted value| /
accepted value) x 100%
Also see Problem Set # 1-14 in the workbook
Precision:
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This is the concept which addresses the degree of
exactness when expressing a particular measurement.
The precision of any single measurement that is made
by an observer is limited by how precise the tool
(measuring instrument) is in terms of its smallest unit.
How would you divide the following 1 meter long bar up
into smaller divisions? Why? What would your choice
have to do with precision?
1 METER BAR
Precision and Measuring:
Significant Digits:
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When someone else has made a
measurement, you have no control over
the choice of the measuring tool or the
degree of precision associated with the
device used.
You must rely on a set of rules to tell you
the degree of precision.
Refer to the “Rules for determining when
zeros are significant” (PS#1-9, workbook)
Significant Digits in Math:
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Use PS#1-10 to check your understanding
of identifying significant digits in
measurements.
See PS#1-11 for the rules about using
significant digits in addition and
subtraction.
See PS#1-11 for the rules about using
significant digits in multiplication and
division. Then go on and do PS#1-12.
Accuracy & Precision
Accuracy means that a measurement is close to the
accepted value.
Precision means that consistent results are obtained.
A measurement can be precisely inaccurate.
Demos:
Balances
Kilogram bathroom scale.
Decigram balance.
Centigram balance.
Analytical balance.
Significant Digits
Significant Digits are those that can be accurately
measured.
The Rule for Sig. Digs. is to round off to
the least accurate number of Sig. Digs.
in the measurement.
A chain is only as strong as its weakest link.
Sample Problems:
How many significant digits are in each of the following?
a. 903.2
e. 90.3
i. 900.0
b. 0.009 0
f. 0.090 0
j. 99
c. 0.007
g. 0.008 0
k. 0.049
d. 0.02
h. 70
l. 5.000 2
Scientific Notation
Scientific Notation means to change your answers
into "Standard Form" which is whole
number then decimal. e.g. 5.29 X 108.
Sample Problems:
Change to scientific notation:
a. 204
f. 23.5 X 105
b. 12.89
g. 0.002 X 10-3
c. 0.007
h. 423.2 X 10-14
d. 0.00569
i. 313 X 108
e. 46359.23
j. 5689 X 10-22
Scientific Notation:
Addition and Subtraction
Round to least precise measurement
 Ex. 24.686 m
2.343 m
+ 3.21_m_
30.239 m
The correct answer is 30.24 m
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Scientific Notation:
Multiplication and Division
Round to least amount of significant
figures
3.22 cm
X 2.1 cm
6.762 cm
The answer would then be 6.8cm
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More Measurement:
Orders of Magnitude-- Powers of Ten
Direct Proportion-up gives up.
Inverse Proportion-- up gives down.
Interpolation-- finding points between points.
Extrapolation-- finding points beyond the last point.
Scalar-gives magnitude only. 50 km/hr.
Vector-- gives magnitude & direction. 50 kph
Northeast. It is represented by an arrow.
Orders of Magnitude
Video: Powers of Ten
Mass vs.
Volume
Linear Relationship
As the volume
increases, so
does the mass.
Inverse Relationship
As the speed
increases, the
time for the
trip decreases.
Terms:
Matter-- has mass and occupies space.
Mass -- quantity of matter measured by inertia.
Inertia-- resistance to change in motion.
Density = mass/volume. i.e.
H20 1g/cc, Fe 8g/cc, Pb 11g/cc, Hg 14g/cc, Au 19g/cc
Energy-- ability to do work.
Potential Energy is stored energy, fuel, wound spring
Kinetic energy is in motion, car zipping along.
Law of Conservation of Matter & Energy-Matter & energy cannot be created nor destroyed
but only changed in form.
E = mc2
Density Problems
D = M/V
D = Density
M = Mass
V = Volume
Find the density of a sample whose mass is 25.0 g and whose
volume is 82.3 cm3.
Find the mass of a sample whose density is 8.2 g/ cm3 and
whose volume is 52.0 cm3.
Find the volume of a sample whose mass is 250 g and whose
density is 6.3 g/cm3.
We Must Practice Physics