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# BASIC CONCEPTS OF EXPERIMENTAL DESIGN

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EXPERIMENTAL DESIGN
DEFINE THE PROBLEM
What is a good question for an
experiment?
One that is testable with the materials at
hand
Now we need a hypothesis to guide
our investigation.
What is a hypothesis?
No, It is NOT an educated guess!
you make might affect another factor.
Tentative or trial solution to the question.
An if вЂ¦вЂ¦вЂ¦вЂ¦ then вЂ¦вЂ¦вЂ¦вЂ¦ statement.
Variables
Variables are things that change.
The independent variable is the variable that is
purposely changed. It is the manipulated
variable.
The dependent variable changes in response to
the independent variable. It is the responding
variable.
Be sure to operationally define each variable.
Constants in an Experiment
What are constants in an experiment?
Factors that are kept the same and not
allowed to change
The Control in an Experiment
What is a control?
The part of the experiment that serves as
the standard of comparison.
Why is a control necessary?
It is the unchanged part of the experiment
that detects the effects of hidden variables.
Materials and Procedures
A description of what you will use for your experiment, and
how you will do it.
Be sure to include:
вЂўLevels of the Independent Variable
вЂўRepeated Trials
вЂўDrawing of Apparatus
Levels of the Independent
Variable
How many different levels of the
independent variable should we test?
3?
5?
10?
The more the better?
Repeated Trials
What are repeated trials?
The number of times that a level of the
independent variable is tested.
Why are repeated trials necessary?
They reduce the possibility of chance
errors affecting the results.
Drawing of Experiment
Include Labels
to clearly
identify the
important parts
of the
experimental
setup
Qualitative Observations and
Results
What are qualitative
observations?
They are what you perceive that
occurred during the course of your
experiment. They are
identification of trends in the data.
Quantitative Observations and
Results
What are quantitative observations?
Numbers in the form of raw data displayed
in data tables and graphs
Sample Data Table
Title: The Effect of the independent variable on the
dependent variable
Column for
independent variable
Label вЂ“ with units if
necessary
Column for
dependent variable
Column for derived
quantity
Label вЂ“ with units if
necessary вЂ“ multiple trials
included
Label вЂ“ with units if
necessary. Example
= average of trials
1
2
3
0
0
1
0
0
1
3
5
4
4
2
6
4
7
6
3
7
6
8
7
4
9
9
8
9
WhatвЂ™s wrong with this table?
Number scoops of
calcium chloride
Temp. Change of
water (oC) Trials
1
2
Average temp. change
(oC)
3
0
0
1
0
0
2
3
5
4
4
4
6
8
7
7
6
11
11
8
10
8
10
14
17
15
18
14
16
14
17
WhatвЂ™s wrong with this table?
The Effect of Various Amounts of Calcium Chloride on
the Temperature of Water
Number scoops of
calcium chloride
Temp. Change of
water Trials
1
2
Average temp. change
3
0
0
1
0
0
2
3
5
4
4
4
6
8
7
7
6
11
11
8
10
8
10
14
17
15
18
14
16
14
17
WhatвЂ™s wrong with this table?
The Effect of Various Amounts of Calcium Chloride on
the Temperature of Water
Number scoops of
calcium chloride
Trials
1
2
Average temp. change
(oC)
3
0
0
1
0
0
2
3
5
4
4
4
6
8
7
7
6
11
11
8
10
8
10
14
17
15
18
14
16
14
17
Constructing a Graph
What is the purpose of a graph?
Graphs communicate in pictorial form the
data collected in an experiment
Graphs
Title: The Effect of the independent variable on the dependent
variable
Dependent
Variable вЂ“ include
units and an
appropriate scale
Independent Variable вЂ“ include
units and an appropriate scale
Bar vs. Line Graphs - Which Should I Use?
The type of graph to use depends on the type of
data collected.
Two kinds of data: Discrete and Continuous
Discrete data are categorical like days of the week,
color, and brand of battery. Intervals between the
data have no meaning. USE A BAR GRAPH
Continuous data are associated with measurements
involving a standard scale. Measurements should be
able to show a trend or relationship. Intervals
between data have meaning.
USE A LINE GRAPH
Constructing a Graph
DRAW AND LABEL
AXES
Amount of Calcium Chloride (scoops)
X Axis - Independent Variable
Constructing a Line Graph - DETERMINE SCALES
FOR AXES
Increase values on axes by 1, 2 ,5, 10 or
20
multiples of 10. There should be about
5 numbered subdivisions on each axis.
15
X: Largest value вЂ“ Smallest value = Range
10 scoops - 0 scoops = 10 scoops
10
10 scoops divided by 5 = 2
5
Y: Largest value вЂ“ Smallest value = Range
17 oC вЂ“ 0 oC = 17 oC
scoops
17o C divided by 5 = 3.4 or ~ 5 oC
0
0
2
4
6
8
10
Amount of calcium chloride (scoops)
Constructing a Line Graph вЂ“ PLOT DATA PAIRS
20
15
10
5
0
.
.
.
.
.
.
Data Pairs
0
2
4
6
8
10
Amount of calcium chloride (scoops)
(0, 0)
(2, 4)
(4, 7)
(6, 10)
(8, 14)
(10, 17)
Constructing a Line Graph вЂ“ DRAW A
LINE-OF-BEST-FIT
20
15
10
5
0
.
0
.
.
2
4
.
6
.
8
.
10
Amount of calcium chloride (scoops)
Constructing a Line Graph вЂ“ TITLE THE GRAPH
AMOUNTS OF CALCIUM CHLORIDE
ON THE TEMPERATURE OF WATER
20
15
10
5
0
.
.
.
.
.
.
The title should state
the effect of the
independent variable
on the dependent
variable.
0
2
4
6
8
10
Amount of calcium chloride (scoops)
Q1- What is wrong with this graph?
20
THE EFFECT OF ADDING VARIOUS AMOUNTS
OF CALCIUM CHLORIDE ON THE
TEMPERATURE OF WATER
15
10
5
0
.
.
.
.
.
.
0 1 2 3 4 5 6 7 8 9 10
Amount of calcium chloride (scoops)
Q2 - What is wrong with this graph?
AMOUNTS OF CALCIUM CHLORIDE ON
THE TEMPERATURE OF WATER
17
14
10
7
4
0
.
.
.
.
.
.
0
2
4
6
8
10
Amount of calcium chloride (scoops)
Q3 - What is wrong with this graph?
AMOUNTS OF CALCIUM CHLORIDE ON
THE TEMPERATURE OF WATER
20
15
10
5
0
.
0
.
.
.
.
2
4
6
8
Amount of calcium chloride
.
10
Q4 - What is wrong with this graph?
10
8
6
4
2
0
.
AMOUNTS OF CALCIUM CHLORIDE ON
THE TEMPERATURE OF WATER
.
.
.
.
.
0
5
10
15
20
Average Temp. Change (oC)
25
Q5 - What is wrong with this graph?
AMOUNTS OF CALCIUM CHLORIDE ON
THE TEMPERATURE OF WATER
20
15
10
5
0
.
.
.
.
.
.
0
2
4
6
8
10
Amount of calcium chloride (scoops)
Q6 - What is wrong with this graph?
20
15
10
5
0
.
.
.
.
.
.
0
2
4
6
8
10
Amount of calcium chloride (scoops)
Q7 - What is wrong with this graph?
40
AMOUNTS OF CALCIUM CHLORIDE
ON THE TEMPERATURE OF WATER
30
20
10
0
..
..
..
0
10
20
30
40
50
Amount of calcium chloride (scoops)
Analysis and Interpretation of
Results
This is where you describe in words
what is illustrated by your data as
shown in your table and graph
You also describe the meaning of the
results
Possible Experimental Errors
What factors in your
materials or procedure might
have had an impact on your
results?
Conclusion
Why or why not your results supported or
did not support the hypothesis.
Hypotheses are never вЂњwrongвЂќ. They are
either supported or not supported.
Include reasons for the hypothesis to be
supported or unsupported.
Recommendations for Further
Experimentation
What are some practical applications
What other questions that could be
Writing A Statement of
the Problem for the
Experiment
What should it state?
It should state: вЂњThe Effect of the Independent
Variable on the Dependent VariableвЂќ.
What is a good statement of the problem
for вЂњThe Helicopter?
What is the effect of wing length on time of descent?
The independent variable is the variable that is
purposely changed. It is the manipulated variable.
The dependent variable changes in response to the
independent variable. It is the responding variable.
What is the вЂњHelicopterвЂќ independent variable?
length of one wing as measured in centimeters
What is the dependent variable?
time of descent as measured in seconds
Title for the Helicopter
Experiment
The Effect of Wing Length on the Length
of Time the Helicopter Takes to Reach
the Ground
Another Look
at Our Hypothesis
INDEPENDENT VARIABLE
If the length of the wings are increased,
DEPENDENT VARIABLE
then time of descent will increase.
Constants in an Experiment
Factors that are kept the same and not
allowed to change
What should be kept constant in theвЂњHelicopterвЂќ?
CONSTANTS
Same structure of helicopters
Same dropping technique
Same dropping height
The Control in an Experiment
The part of the experiment that serves
as the standard of comparison.
What is a good control for the вЂњHelicopterвЂќ?
CONTROL
Beginning length of wings (5 cm)
Levels of the Independent
Variable
How many different levels of the
independent variable should we test?
Enough to clearly illustrate a trend in
the data - 5cm, 6cm, 7cm, 8cmвЂ¦..
Repeated Trials
How many repeated trials are needed in the
вЂњHelicopterвЂќ?
At least 3, then calculate an average value
for each level of the independent variable
Drawing of Experiment
Hold helicopter
in the middle
Drop from
same spot
each time
Qualitative Observations and Results
вЂўAs we dropped the helicopter, we
observed that sometimes they
seemed to be affected by air
currents.
вЂўIt appeared that helicopters with
longer wingspans took a greater
time to reach the ground
Quantitative Observations
Data Table and Graph
Sample Data Table
Title: The Effect of wing length on the time of descent
Descent Time (s)
Wing Length
Trials
Average Descent
Time (s)
(cm)
5
1
3
2
5
3
4
6
4
5
6
5
7
6
7
5
6
8
7
8
6
7
9
9
7
8
8
4
The Effect of Wing Length on Descent Time
.
8
.
7
.
6
.
5
4
.
5
6
7
8
Wing Length (cm)
9
The Effect of Wing Length on Descent Time
8
.
.
.
.
6
4
.
2
0
0
2
4
6
8
Wing Length (cm)
10
Analysis and Interpretation of
Results
While individual trial results showed some
variation; overall, as average wing length
increased from 5 through 9 centimeters,
average time of descent also increased
from 4 through 8 seconds.
This shows a direct correlation.
Possible Experimental Errors
Although the average results supported the
hypothesis, the individual trial results showed
some variation. Some possible reasons for this
could be due to air currents in the room or
reaction time differences between the timer
and the helicopter dropper.
Conclusion
The overall results supported the
hypothesis.
A possible reason for this could be
due to increased surface area of the
wing in contact with the air - allowing
for greater air support.
Recommendations for Further
Experimentation/ Practical Applications
Increased time of descent due to greater wing length
suggests that increased wing length could lead to
greater fuel efficiency of an actual helicopter.
Other experiments investigating factors that would
contribute to greater descent time might include:
making modifications in the shape of the wings,
changing the number of wing blades, and making folds
Authors
Harry Dillner, Kathy Melvin