Chapter 1: Measurement

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Chapter 1 Measurement
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The Metric System Many properties of matter are
quantitative
This means that matter can be measured
Measured quantities of matter must always be
specified in units
The units used for scientific measurement are
those of the metric system
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Units of the Metric System
The metric system is a base-ten decimal system
Each unit is ten times larger than the next
smaller unit
In 1960, an international system of metric units
was agreed upon for use in scientific measurement
These units are called SI units
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SI Base Units
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Prefixes used in the metric system
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Metric Conversions using Dimensional Analysis
The key to using dimensional analysis is the
correct use of conversion factors
What is a conversion factor?
A conversion factor is a fraction whose numerator
and denominator are the same quantity expressed
in different units
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Example of a conversion factor Inches to
centimeters
Both the numerator and the denominator are
expressing the same quantity of length using
different units
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When using conversion factors, we want the given
units to cancel Then we end up with the desired
units
Unit
Example Using conversion factors, convert 6.25
inches to centimeters
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Step 1 Use our inches-to-centimeters conversion
factor
Question Which one do we use?
or
?
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Answer We want the desired unit in the numerator
of the conversion factor
Step 2 Set up the calculation like this
The inch units cancel, and we are left with
centimeters, our desired unit
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Lets use conversion factors to express 2.6
meters as millimeters
Here are the conversion factors we need
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Always set up your calculations so that given
units cancel, and you get the desired units at
the end
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Scientific Method
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Science is a process of inquiry that includes
repeatable observations and testable hypotheses
This process blends two main types of reasoning
Inductive reasoning and hypothetico-deductive
reasoning
Most scientists practice a combination of both
The word science is derived from a Latin verb
meaning to know
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Science and Induction
Scientific investigation can lead to important
conclusions based on a type of logic called
inductive reasoning
An inductive conclusion is a generalization that
summarizes many concurrent observations
Observation
General Principle
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Example All the swans at Lake Mead are white in
color All the swans at Lake Powell are white in
color All the swans at Lake Michigan are white in
color All the swans at Lake Okeechobee are white
in color Argument Therefore, all swans are
white
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This is inductive reasoning The argument that
all swans are white is a generalization made from
many specific observations
Observation
General Principle
There is a big problem with this argument
What is it?
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If someone finds a black swan at another lake
somewhere, our argument, or theory, is no longer
valid
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Hypothetico-Deductive Science
Hypothetico hypothesis-generating
Deduction Another form of logic
Recall A hypothesis is a tentative answer to
some question
Deductive logic differs from inductive logic When
using deductive logic, we go from the general to
the specific
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Deductive logic differs from inductive
logic When using deductive logic, we go from
general premises to specific conclusions
Who is this guy?
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This is Socrates, and well use him in an example
of deductive logic
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All men are mortal Socrates is a man Therefore,
Socrates is mortal
Or
All organisms are composed of tiny cells Socrates
is an organism Therefore, Socrates is composed of
tiny cells
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General Premises
Specific Conclusion
In the process of science, the deduction usually
takes the form of predictions about what the
outcomes of our experiments or observations
should be
We then test the hypothesis by performing an
experiment to see whether or not the results are
as predicted
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As a formal process of inquiry, the scientific
method consists of a series of steps. Most
science is far less structured than presented
here.
The key element here is the use of
hypothetico-deductive reasoning.
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My flashlight doesnt work
Hypothetico-Deductive Reasoning
Whats wrong with my flashlight?
The batteries are dead
If I my hypothesis is correct
and I replace the batteries
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Then
My flashlight should work!
But what if my flashlight still doesnt work?
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We can always generate alternative hypotheses and
test them in the same manner
Alternative hypotheses The bulb is burned
out The contacts are corroded The on-off switch
is broken
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The point here is that any one of these
hypotheses can be tested according to the
scientific method It is also important to note
that all these hypotheses are falsifiable under
the scientific method Remember our theory about
the swans according to the scientific method we
look for evidence that disproves our theory One
black swan can disprove our theory that all swans
are white
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Experimental
Design
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Experiments
In order to test a hypothesis we must design a
suitable experiment
When performing our experiment, we must look for
results relating to our hypothesis
These results will either support or not support
our hypothesis
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I want to conduct an experiment to identify
essential nutrients required in plants
I will use plants grown hydroponically (in water
rather than soil)
One group of plants will grow in an aqueous
solution of complete nutrients
Another group of plants will grow in a solution
lacking one nutrient
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Hydroponic Farming
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Our plants growing in a complete nutrient
solution is called the control group
Our plants growing in a solution missing one
nutrient is called the experimental group
The control group allows us to compare with the
experimental group
If the missing nutrient has an effect on the
experimental plants, their appearance should be
different than the control group plants
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What about the variables?
For our experiment to succeed, we must identify
all of the variables
One variable is the growth response of the plants
in the incomplete nutrient solution
Another variable is the difference in the
experimental nutrient solution
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The incomplete nutrient solution is the variable
that we, as investigators, are manipulating
We call this variable the independent variable
We will measure the effect of the independent
variable on the growth of the plants
The response of the plants to the altered
nutrient solution is called the dependent variable
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We call the response of the plants the dependent
variable because the magnitude of the response
depends on how we manipulate the independent
variable
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Homework for Next Week
Chapter 1 Answer questions 1 12 on pages 17
and 18. Chapter 2 Answer questions 1 7 I will
collect all homework next week during class
Before coming to class, read the lab ahead of
timeBe Prepared!