The Scientific Method & Experimental Design

Report
The Scientific Method &
Experimental Design
Integrated Science: Intro to Physics
Prepared by Mr. D. McCallister
Modified by Mr. R. Moleski, Ph.D.
The Scientific Method
•
•
•
•
•
•
•
•
Ask a question
Research the Subject – Library Research that is
Formulate a Hypothesis
Design and conduct the Experiment
Collect and Analyze data
Make a tentative Conclusion
Test the Conclusion
Repeat the Experiment…….Why?
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Variables
• Properties that change during an experiment
• Can be
– Independent
• this variable is changed by the experimenter
– Dependent
• this variable changes because of the independent
variable
• All other properties should be held constantthey are called Controlled Variables.
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Units of Measure
• Original Metric Units
– Distance – meter (m)
– Time – seconds (s)
– Mass – kilograms (kg)
• SI Units (these 7 are the basis for all others)
– Temperature – kelvins (K)
– Electric Current – ampere (A)
– Light Intensity – candela (cd)
– Amount of a Substance – mole (mol)
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Dimensional Analysis & Unit
Conversion
What is dimensional analysis?
• A tool that allows us to change units
and solve problems.
10 km = ?? mi
1 mi = 1.604 km
1mi )= 6.23 mi
10 km(___________
1.604
m km
Flashback
• Convert 87 cm into m using the Factor-Label
technique using conversion units and
cancelling units.
o (1 cm = 10-2 m)
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Terms, terms, terms…
• fact
– a close agreement by competent observers who
make a series of observations of the same
phenomenon.
– revisable data about the world
• laws (a.k.a. principles)
– hypotheses and facts that are tested over and
over again without being contradicted
– not as descriptive as theories
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Terms, terms, terms…
• theory
– a synthesis of a large body of information
– not judged as “true or not true,” rather as “useful
or not useful”
– interpret facts
• concept
– intellectual framework that is part of a theory
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Terms, terms, terms…
• hypothesis
– an educated guess
– to be scientific hypothesis, must be testable
– must have a test for rightness, and a test for
wrongness
– Which of the following are scientific?
• The universe is surrounded by a second universe, the
existence of which cannot be detected by scientists.
• Albert Einstein was the greatest physicist of the
twentieth century.
• Atoms are the smallest particles of matter.
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Making Hypotheses!
• Complete all questions, in groups if you want.
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Analyzing Variables
Height (cm)
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Shoe Length (cm)
Wingspan (cm)
Intro to Physics: Scientific Inquiry
Stride Length (cm)
14
Review of Last Week
• Tuesday: What is physics?
– the study of the interactions of mass and energy
• Wednesday: Scientific Method, Units of Measure,
Factor Label
– length (meter), time (second), mass (kilogram)
– metric prefixes
– converting between units using factor-label
• Thursday: Making Hypotheses
– theories, facts, laws
• Friday: Analyzing Variables
– Was there a relationship between height and other body
characteristics?
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Preview of this week:
• Today:
– laboratory safety, scientific notation
• Tuesday:
– Charts & Graphs
• Wednesday
– Accuracy, precision, sig figs
• Thursday
– Review
• Friday
– Exam on Scientific Inquiry
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Laboratory Safety Procedures
• Wear the right clothing for lab work.
– No open-toe shoes!
• Do not perform unauthorized experiments or
use equipment and apparatus in a manner for
which they were not intended.
• No horseplay in the lab.
• Never work alone in the lab.
• Follow fire drill procedures when fire alarm
sounds.
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Fire Alarm Procedures
• Exit the room and turn right, then left to exit
the building near the main office.
• Meet the class halfway down the parking lot
on the right.
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Electricity Lab Safety Procedures
• Do not use electrical equipment with frayed or
twisted wires.
• Be sure your hands are dry before using
electrical equipment
• Do not trip over electrical cords.
• Use extreme caution when working with hot
plates or other heating devices.
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Stop to Think…
• Which of the following are allowed in the lab?
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Scientific Notation
• Is there an easier way to express large
numbers?
– Ex)
2 3471693273 . x 10
23,471,693,273
10 places
This
Count
number
the decimal
number
becomes
Move
the
the
of decimal
exponent
places
of ten.
point
so that
there
Moving
you
moved
the nondecimal
the
is
only
one
left
decimal
makes
it positive,
zero
digitpoint.
on
the
right
left ofmakes
it. negative.
Stop to Think…
• Place the following numbers into scientific
notation.
– 93,000,000
– 3,600
– 0.00015
– 0.453
– 152
– 63
–9
Metric Prefixes
Power
10-18
10-15
10-12
10-9
10-6
10-3
10-2
10-1
* rarely used
Prefix
attofemtopiconanomicromillicentideci-
Symbol
a
f
p
n
µ
m
c
d
Power
101
102
103
106
109
1012
1015
1018
Prefix
dekahectokilomegagigaterapetaexa-
Symbol
da*
h*
k
M
G
T
P*
E*
The Nature of Measurement
• Consider the following reading on a meter
stick:
1
cm
2
3
4
5
6
7
8
Error
• Random
– can be reduced with repeated readings
• Systematic
– cannot be reduced with repeated readings
– always in same direction (high or low)
Precision vs. Accuracy
• Accuracy is how close readings or calculations
are to the true or accepted value.
• Precision is how many decimal places an
instrument resolves.
• To illustrate this…. a challenge of archery!!!!
Precision vs. Accuracy
x xxxx
xx
True or
accepted value
Precise, but not accurate!
Precision vs. Accuracy
x
x
x
x
x
x
x
x
Accurate, but not precise!
Precision vs. Accuracy
x
x
x
x
x
x
x
Neither accurate nor precise!
Precision vs. Accuracy
xxx
xxxx
Both accurate and precise!
So what’s the difference?
• Accuracy is how close a measurement is to the
true or accepted value
• Precision is how close repeated
measurements are to each other
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How many decimal points do I record?
• Always all the measured digits, and one
estimated
• For graduated instruments (meter stick, spring
scales)
– Record to half the smallest marking (estimate 0.5 mm
on a meter stick)
• For digital instruments
– Record the measurement given, exactly as it is shown
• ex) If a digital scale reads 1.600 g, then record 1.600 g, not
1.6 g.
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Stop to Think…
• Which is more precise, the metric side of a
meter stick or the inches side?
• What could affect the accuracy of a meter
stick?
Sig Figs
• If numbers given in a problem aren’t precise,
then our answer shouldn’t be either!
• There are rules for adding & subtracting sig
figs
– demonstration
• There are yet more rules for multiplying &
dividing sig figs!
– demonstration
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Stop to Think
• What is the correct measurement for the
length of the blue rectangle?
1
2
3
4
5
6
7
8
cm
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Modeling
• It is often helpful to simplify real-world
phenomena in order to understand it better.
• A model is a simplification of reality that
allows us to understand a situation better.
• It is NOT real-life, but a simplification of reallife.
• In a word: models are SIMPLIFICATIONS!
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The Physics of Christmas
A Great Example of Modeling
• No known species of reindeer can fly.
• But there are 300,000 species of living
organisms yet to be classified, and while most
of these are insects and germs, this does not
COMPLETELY rule out flying reindeer which
only Santa has ever seen.
• Santa has 31 hours of Christmas to work with,
thanks to the different time zones and the
rotation of the earth, assuming he travels east
to west (which seems logical).
• There are 2 billion children (persons under 18)
in the world.
• BUT since Santa doesn't (appear) to handle
the Muslim, Hindu, Jewish and Buddhist
children, that reduces the workload to 15% of
the total - 378 million according to Population
Reference Bureau.
• At an average (census) rate of 3.5 children per
household, that's 91.8 million homes.
• One presumes there's at least one good child
in each.
• This works out to 822.6 visits per second.
• This is to say that for each Christian household
with good children, Santa has 1/1000th of a
second to park, hop out of the sleigh, jump
down the chimney, fill the stockings, distribute
the remaining presents under the tree, eat
whatever snacks have been left, get back up
the chimney, get back into the sleigh and
move on to the next house.
• Assuming that each of these 91.8 million stops
are evenly distributed around the earth
(which, of course, we know to be false but for
the purposes of our calculations we will
accept), we are now talking about .78 miles
per household, a total trip of 75-1/2 million
miles, not counting stops to do what most of
us must do at least once every 31 hours, plus
feeding and etc.
• This means that Santa's sleigh is moving at
650 miles per second, 3,000 times the speed
of sound.
• For purposes of comparison, the fastest manmade vehicle on earth, the Ulysses space
probe, moves at a poky 27.4 miles per second
- a conventional reindeer can run, tops, 15
miles per hour.
• The payload on the sleigh adds another
interesting element.
• Assuming that each child gets nothing more
than a medium-sized Lego set (2 pounds), the
sleigh is carrying 321,300 tons, not counting
Santa, who is invariably described as
overweight.
• On land, conventional reindeer can pull no
more than 300 pounds. Even granting that
'flying reindeer' (see point #1) could pull TEN
TIMES the normal amount, we cannot do the
job with eight, or even nine.
• We need 214,200 reindeer.
• This increases the payload - not even counting
the weight of the sleigh - to 353,430 tons.
• Again, for comparison - this is four times the
weight of the Queen Elizabeth cruise ship.
• 353,000 tons traveling at 650 miles per second
creates enormous air resistance - this will heat
the reindeer up in the same fashion as
spacecraft re-entering the earth's
atmosphere.
• The lead pair of reindeer will absorb 14.3
QUINTILLION joules of energy.
• Per second.
• Each.
• In short, they will burst into flame almost
instantaneously, exposing the reindeer behind
them, and create deafening sonic booms in
their wake.
• The entire reindeer team would be vaporized
within 4.26 thousandths of a second.
• Santa, meanwhile, will be subjected to a
centrifugal effect that is 17,500.06 times
greater than gravity.
• A 250-pound Santa (which seems ludicrously
slim) would be pinned to the back of his sleigh
by 4,315,015 pounds of force.
• But all this is irrelevant, since Santa is
magic!!!!
• THE END!!!!
• Tinyurl.com/mcphysics
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Metric Prefixes
Power
10-18
10-15
10-12
10-9
10-6
10-3
10-2
10-1
* rarely used
Prefix
attofemtopiconanomicromillicentideci-
Symbol
a
f
p
n
µ
m
c
d
Power
101
102
103
106
109
1012
1015
1018
Prefix
dekahectokilomegagigaterapetaexa-
Symbol
da*
h*
k
M
G
T
P*
E*

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