# A Controlled Experiment

```Bellringer
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Define these words: (use Ch 1 of your book)
Science
Scientific methods
Hypothesis
Controlled experiment
Variable
A Controlled
Experiment
Part of the scientific method
Review-Scientific Method
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Problem/ Question
Observations/Research
Hypothesis
Experiment
Data/Results
Conclusion
Communicate Results
Variables
A controlled experiment tests only one variable and all
other factors remain the same.
 Variable: A factor that can change. A variable can
change other factors when it changes.
Examples of variables:
-Temperature
-Light
- Open vs. Closed container
-Location
-Time
-Elevation
-Pressure
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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.
Independent vs. Dependent
Variables
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The dependent variable is a factor that changes
because the independent variable changes. However
the independent variable is not changed by the
dependent variable.
Example: Elevation and Boiling temperature of water.
The boiling temperature of water changes because of
changes in elevation. Changes in the boiling
temperature of water do not change elevation.
Constants or Controlled Variables
in an Experiment
What are constants in an experiment?
Factors that are kept the same and not
allowed to change.
It is important to control all but one
variable at a time to be able to
interpret data
Control
-A variable or factor that does not change in the
experiment. It remains constant.
In a Controlled experiment only one variable is
allowed to change at a time. Everything else
remains constant.
Experimental Error
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Bias (what you expect to happen prevents you
from observing what actually happens)
Testing more than one independent variable.
Not having a control group.
Not having constants.
Not using a large enough test group.
Not repeating the experiment enough times.
Francisco Redi &amp; Spontaneous
Generation
OBSERVATIONS: Flies land on meat that is left uncovered. Maggots appear on the meat.
HYPOTHESIS: Flies produce maggots.
VARIABLES
Covered jars
Uncovered jars
Controlled Variables:
jars, type of meat,
location, temperature,
time
After several
days
Independent Variables:
gauze (keeps flies away from
meat)
Dependent Variable:
whether maggots
appear
Maggots appear
No maggots appear
CONCLUSION: Maggots form only when flies come in contact with meat.
Spontaneous generation of maggots did not occur.
Replicates
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In an experiment multiple copies of the
experiment are done at the same time.
This is to ensure that the results are accurate
(true) and not due to a mistake, error or chance
event.
Treatments
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Set of variables in the experiment that are the
same in each group of replicates.
2 Treatments
Covered
Uncovered
Problem
Which pinto beans will grow
better, those in fresh water or
salt water?
Review
What is a controlled experiment?
• An experiment with one group of test subjects
being exposed to the variable, and one that is not
variable being tested!
treated with the _________
What is the variable being tested in the pinto bean
experiment?
Salt (How it EFFECTS the
pinto bean growth)
Controlled Experiment
What are the groups in a controlled experiment?
Control Group
Experimental Group
-Gets NORMALTreatment
(No Variable).
-Used for comparison
Gets the VARIABLE
you are testing.
In the pinto bean experiment, which is the control
group and which is the experimental group?
Control Group:
Fresh water beans
Experimental Group:
Salt Water Beans
Controlled Experiment Variables
Variables: factors that can change
What are the two types of variables?
1.
2.
Independent (manipulated)–is what the
scientist controls or changes or it affects
something. (SALT Affects Bean Growth)
Dependent (responding)–is the variable that
is observed and that is affected by the
independent variable. (BEAN GROWTH)
Experiment (Controlled)
Constants
Constants: are exactly the same for both the
control and experimental groups. Both groups
should be treated exactly the same except for the
variable being tested.
What are the constants in the pinto bean
experiment?
• Beaker Size
• Amount of Water
• Brand of Pinto Beans
Exit Assignment
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Identify the variables in this experiment:
Can tomato plants grow without being exposed
to sunlight?
What is the independent variable? Dependent
variable? Constants?
How would you set up the experiment to test
this question?
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