Parts of a Controlled Experiment

Parts of a Controlled Experiment

A controlled experiment is an experiment in which the scientist changes/manipulates only one thing to observe and measure the effects of that one change.  Below is an outline of the parts of every controlled experiment.  In order to begin developing scientific questions for designing our own controlled experiments, we must fully understand the parts of every controlled experiment.  

• Independent Variable (IV)/Experimental Group (EG): The one part of the experiment that is changed/manipulated or given different treatment by the scientist (cause).
• Dependent Variable (DV): The part of an experiment that changes in response to, or affected by, the independent variable.  This change is what the scientist observes and measures throughout the experiment (effect).
• Constants (C): The parts of an experiment that are kept the same for all groups and trials to ensure a fair test.
• Control Group (CG): The group in an experiment that is “normal” or untreated to be compared with the experimental group.  Keep in mind that there is not a control group in every experiment.  There is only a control group if there is such thing as a "normal" or untreated condition.

Key words for Identifying the Parts of a Controlled Experiment

The following key words can help you to identify the parts of a controlled experiment.

• Independent variable – different, change, varied/various, compare, cause, manipulate, experimental group, experimental variable
  
• Dependent variable – measure, record, results, effect, outcome, response
• Constants – same, similar, identical, replicate, clone, copy
• Control Group – normal, untreated, natural, regular, typical

Re-watch the video below on the parts of a controlled Experiment:

Every controlled experiment investigates how an independent variable (the one thing changed by the scientist) has an effect on the dependent variable (what the scientist measures and observes).  

In-Class Activity

Part I
Answer the questions below using the video and your notes from class.  Write the questions and answer them in complete sentences.  

1.  Fill in the blanks to write the scientific, testable question under investigation FROM THE VIDEO.    
What is the effect of the type of drink on _______________?
2.  What is the independent variable in this controlled experiment? (from the video)
3.  What is the dependent variable in this controlled experiment? (from the video)
4.  What does "DRY MIX" stand for?

Part II
Take a look at the two scientific questions below.  These questions were designed and tested by middle school students in New York City.  They are not by any means perfect controlled experiments, but they do provide examples of how a student scientist studies how making one change (independent variable) has a measurable effect on something else (dependent variable).  You may click on the question to see the details of the entire project.  After reviewing these two projects, answer the questions that follow.

• What is the effect of air pressure on how high a basketball bounces?
• How does the amount of baking soda affect the the explosion of a volcano?

1.  Identify the independent variable (IV), dependent variable (DV), constants (C), and control group (if there is one) for the two question above.

• What is the effect of air pressure on how high a basketball bounces?

           IV: ______________________________
           DV: _____________________________
           C: ______________________________
           CG: _____________________________

• How does the amount of baking soda affect the the explosion of a volcano?

           IV: ______________________________
           DV: _____________________________
           C: ______________________________
           CG: _____________________________

2.  What two parts of a controlled experiment (among IV, DV, C, and CG) are included in the actual questions for each experiment above?  

3.  Rewrite the questions above, but replace the independent variable in the example with "IV", and dependent variable with "DV".  

For example, "How does the amount of water affect the height of a fig plant?
"How does the    (IV)       affect the      (DV)       ?"