1-5 Designing an Experiment

The Tools of Science- Comprehensive Science 3Mrs. Bloch

VocabularyScientific 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. 34Orbiting 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? ___________________

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1. Why do you think the scientists grew cuttings both in space and on Earth? _______________________________________________

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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.

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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 VariablesThe 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

Figure 3 – Controlling VariablesA student wants to test whether shampoo cleans oily hair better than water alone. The student mixes oil with water in one test tube and oil with soapy water in another test tube. 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?

Amount of Soap in Water (mL)

Time of Oil and Water Separation (seconds)

0 15

1.5 105

Designing a Controlled ExperimentA 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 BiasWhen 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? ___________________________

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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. 39Percentage of Students Finished Testing Over TimeInformation 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. 40A 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 WeeklyImagine 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?

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b. Explain- Why is a hypothesis important even if evidence fails to support it? ______________________________________

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I get it! Now I know that you test a hypothesis by ____________

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What is a Scientific Explanation? Pg. 42In 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?

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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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