The Tools of Science- Comprehensive Science 3
Mrs. Bloch
1-5 Designing an Experiment
Vocabulary
Scientific inquiry-The ongoing process of discovery in science, the
diverse ways in which scientists study the natural world and propose
explanations based on evidence they gather.
Hypothesis-A possible explanation for a set of observations or answer
to a scientific question, must be testable.
Independent variable-The one factor that a scientist changes during an
experiment, also called the manipulated or test variable
Dependent variable-The factor that changes as a result of changes to
the independent variable in an experiment, also called the
responding variable.
Controlled experiment-An experiment in which only one variable is
manipulated at a time.
Vocabulary
Bias-A subjective belief that affects a person’s attitude toward
something, an error in the design of an experiment that affects
the results of the experiment.
Repeated trial (repetition)-A repetition of an experiment to test
whether the experiment’s results support the hypothesis.
Replication-An attempt to repeat a scientist’s experiment by a
different scientist or group of scientists.
Scientific explanation-A generalization that makes sense of
observations by using logical reasoning.
My Planet Diary pg. 34
Orbiting Earth is an amazing experience. But eating dehydrated space
food can be boring and unappetizing. So, scientists conducted an
experiment to see whether they could grow vegetables in space.
They picked an old Thanksgiving favorite: sweet potatoes. They
grew some cuttings onboard a shuttle and some cuttings on Earth.
The cuttings were placed under similar conditions in space and on
Earth for five days. They discovered that the number of roots that
sprouted were the same in both places. But the roots of those in
space actually grew faster! The cuttings that grew in space had
more sugar and starch than those on Earth. Astronauts, however,
hope that space potatoes taste just as good!
1. What was the purpose of the experiment? ___________________
________________________________________________________
1. Why do you think the scientists grew cuttings both in space and on
Earth? _______________________________________________
________________________________________________________
How Do You Conduct A Scientific Inquiry? Pg. 35
Scientific inquiry is the process through which scientists ask and
answer questions about the natural world.
People conduct scientific inquiry by gathering evidence about
the natural world and proposing explanations based on this
evidence.
Posing Questions and Defining a Problem pg. 35
The first steps in the scientific inquiry process are:
posing questions
(why is my milk sour?)
defining a problem
(What made the milk go bad so quickly?)
researching that problem
(Use reference materials to find out why)
Next, develop a hypothesis, a possible answer to a scientific
question.
(If milk is left at room temperature for too long, then it will turn sour)
Assess Your Understanding? Pg. 36
1a. Pose Questions-Write a question about what causes cavities
that could be tested with a scientific investigation.
___________________________________________________
_________________________________________________
b. Develop Hypotheses- Write a hypothesis that might explain
why some people get more cavities than other people.
___________________________________________________
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I get it! Now I know that people conduct scientific inquiry by
___________________________________________________
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How Do You Test A Hypothesis? Pg. 37
You test a hypothesis by designing an experiment that
follows reliable scientific principles.
A large part of designing an experiment is controlling variables.
Controlling Variables
The one factor that is purposely changed to test a hypothesis is the
independent variable or test variable. (air temperature)
The factor that may change in response to the independent variable is
the dependent variable or responding variable. (the time it
takes the milk to sour)
Controlling Variables pg. 37
Amount of
Time of Oil
Figure 3 – Controlling Variables
Soap in
and Water
A student wants to test whether shampoo
Water (mL)
Separation
cleans oily hair better than water alone. The
(seconds)
student mixes oil with water in one test tube
0
15
and oil with soapy water in another test tube.
1.5
105
She watches to see when the mixture
separates.
1. Classify- What is the independent variable? What is the
dependent variable?
2. Identify- Name two other possible variables in this experiment..
3. Draw Conclusions- Write a summary of what was observed in this
experiment. What can you conclude?
Designing a Controlled Experiment
A scientific experiment in which only one variable is tested at a time is
called a
controlled experiment.
If the variables in an experiment are not controlled, it is impossible to
tell which variable influenced the results.
Eliminating Bias
When designing experiments, scientists also have to be careful not to
introduce bias, or an error in the design of the experiment.
 To eliminate bias, scientists use a good sample size and
repeat experiments.
Fig. 4- Virtual Lab – A Controlled Experiment pg. 38
In this experiment, the temperatures must be different enough that
your results can only be due to temperature.
1. Design Experiments- Label each milk sample with the temperature
at which it could be tested. (Hint: Average room temp. is 22 C)
A_________ B__________ C____________
1. Apply Concepts- What is another variable that must be kept the
same for each milk sample? _____________________________
2. Analzye Sources of Error- How could testing milk that is past its
expiration date introduce bias? ___________________________
____________________________________________________
Collecting and Interpreting Data pg. 39
After receiving the results from an experiment, scientists
organize and interpret the data.
Then they examine the data to draw a
conclusion
about whether the data supports the hypothesis.
Before a hypothesis can be accepted as true,
the experiment must be repeated many times with repeated
trials.
Do The Math! pg. 39
Percentage of Students Finished Testing Over Time
Information organized in a data table can easily be made into a graph. This data table shows
the percent of students who finished testing over a period of time.
1. Graph- Plot the data on the graph. Identify the independent and dependent data.
2. Read Graphs- Describe the difference in the percent of students finished testing between 30
and 45 minutes and between 45 and 60 minutes.
3. Challenge- After how many minutes would you predict that all of the students will finish their
testing?
Apply it! Pg. 40
A student dipped squares of nylon, polyester, and cotton in water
and hung them up to dry. He then measured the amount of time
they took to dry.
1. Analyze Experimental
Results- Before the
experiment, the student
hypothesized that nylon
dries the fastest. Do the data support his hypothesis? Explain.
2. Identify Experimental Bias- Are the results from one trial
different from the others? If so, how might the student have
introduced bias that resulted in anomalous data?
3. Apply Concepts- Based on these results what kind of socks
would you want to wear on a fishing trip?
Communicate pg. 41
Florida Science
Weekly
Imagine you conclude
that milk left at room
temperature (22°C)
sours quicker than
refrigerated milk. What
is a catchy newspaper
headline that
communicates this to
other scientists?
Assess Your Understanding pg. 43
2a. Identify- At the beach, a student tests the effectiveness of 3
sunscreens, each with a different sun protection factor. What
is the independent variable in her experiment?
_________________________________________________
_________________________________________________
b. Explain- Why is a hypothesis important even if evidence fails
to support it? ______________________________________
_________________________________________________
I get it! Now I know that you test a hypothesis by ____________
___________________________________________________
What is a Scientific Explanation? Pg. 42
In some branches of science it is difficult to perform controlled
experiments. Scientists in these fields must develop a scientific
explanation.
A scientific explanation is a generalization that makes
sense of observations by using logical reasoning.
Complete Think Pink pgs. 42-43
Does a Flamingo’s diet of shrimp affect the color of its
feathers?
Hypothesis
Variables- I.V.
D.V.
Controls
Procedure
Analysis Info- Skills used
Sources of Error
Alternative Explanations
Assess Your Understanding pg. 43
3a. Summarize How does a scientist explain something when a
controlled experiment cannot be carried out?
___________________________________________________
________________________________________________
b. What tools do scientists use to investigate the natural world?
___________________________________________________
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I get it! Now I know that a scientific explanation is ____________
___________________________________________________
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