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Experimental Design
Experimental Investigation
The organized procedure used to study an aspect of the natural world under controlled conditions
Experimental Design
Testable Question
Research
Hypothesis
Materials/Procedure
Data Collection
Data Analysis
Conclusion
Testable Questions
Asks the question to be answered in an experiment
Includes both the independent variable and the dependent variable
How does ____(Independent Variable)____ affect ___(Dependent Variable)____?
What is the effect of ___(Independent Variable)___ on ___(Dependent Variable)____?
Practice Writing a Testable Question
Using the following information, write a testable question:
Independent variable: hours of studying
Dependent variable: grade earned on a test
Hypothesis
A prediction based on prior knowledge (research) about the expected relationship between the variables in an experiment
Includes both the independent variable and the dependent variable and a reason
Is either supported or rejected by the experiment
Frequently written as an “if…then” statementExample “If the amount of sunlight received by a plant is increased, then the plant will grow taller because plants require sunlight for photosynthesis”
Practice Writing a Hypothesis
Write a hypothesis for the following question:
What is the effect of exercise on a person’s heart rate?
Research
Before beginning an experiment, quality research must be conducted to gather background knowledge
Reliable sources (peer-reviewed journals, textbooks, etc.) *Not wikipedia or blogs*
Also included in the background knowledge are previous observations
Parts of an Experiment
Independent Variable
Dependent Variable
Controlled Variable
Independent Variables
Also called manipulated variables
Changed (manipulated) directly by the scientist
Graphed on the X-axis (horizontal)
Dependent Variables
Also called responding variables
Change as a result of the manipulation of independent variables
Graphed on the Y-axis (vertical)
Controlled Variables
Also called constants
Do not change during an experiment
Must stay the same in order to ensure a fair test
Control Group
A standard or “baseline” group to which the experiment is compared
The independent variable is not changed in the control group
For example, if the scientist is testing how the addition different fertilizers affect a plant’s growth, the control group would be a plant that does not receive any fertilizer
Materials List
List specifically all materials used in an experiment
Include quantities and units
For example, “beakers” is not specific. Instead, write “5 100 mL beakers”
Procedure
A step-by-step guide to conducting an experiment
Procedures must be specific and detailedInclude all tools and materials being used in that step
Procedures should be detailed enough that the experiment can be repeated by another scientist
Organizing Data
Quanitative (numerical) data is organized into tables or charts in rows and columns
Specific independent variables are listed
The number of trials are listed
Blanks are left to fill in measured data (dependent variable)
Title Describing the Data(ex: Independent Variable vs.
Dependent Variable)Trial Independent
Variable 1Independent Variable 2
Independent Variable 3
1
2
3
4
Average
Analyzing Data
Reduce the data: do something to make the amount of data smaller
Central tendencies:Mean
Median
Mode
Range
Frequency
Bar Graphs
Uses rectangular bars of different colors/patterns to display data
Used for comparisons
Line Graphs
Uses points connected by a line to show how values change
Useful for showing trends
Scatter Plots
Uses unconnected points to display data
Useful for showing correlations between variables
Note: correlation does not imply causation!
A correlation between variables does not necessarily mean that one immediately caused the other to change
Positive Correlation
An increase in the variable on the X-axis is associated with an increase in the variable on the Y-axis
Negative Correlation
An increase in the variable on the X-axis is associated with an decrease in the variable on the Y-axis
No Correlation
Random data points – there is no association between the variables
DRY MIX
Dependent
Responding
Y-Axis
Manipulated
Independent
X-axis
Let’s Practice
Title
Independent Variable
Dependent Variable
X
Y
*Don’t Forget*
Every time you make a graph, include:
Descriptive title (ex: Independent Variable vs. Dependent Variable)
Labeled X and Y axes… Include UNITS
Legend (if necessary)
Scale/Interval of axes (3, 6, 9, etc)
Let’s PracticeTime (minutes)
Cart 1 Distance (m)
Cart 2 Distance (m)
Cart 3 Distance (m)
1 1 2 3
2 2 4 6
3 3 6 9
4 4 8 12
A student built three different wooden carts to test the effect of different power sources (battery, wind, and solar) on the speed of her carts. Her data is represented in the table above.
Conclusion
Answers the original question
Restate the hypothesis
Accept or reject the hypothesis and support using evidence from the investigation
Describe relationships in the data
Explain any inferences made using the data
Discuss any problems or sources of error that occurred during the investigation
Discuss any extensions or elaborations on the topic
Publish!
New knowledge is useful when it is shared
Journals, publications, presentations