Unit 1 Scientific Method: Day 11 - Reliability and Constant Variables

·      Reliability: The idea that an experiment should only test one thing at a time.

·      
     TRANSLATION: ONLY one INDEPENDENT VARIABLE!

    

    To do this, scientists are very careful to do two things:

• ·      Keep variables constant___________
• ·      Do the experiment multiple times______

     Think back to our paper airplane experiment:         

1. What were some variables that we needed to keep constant in our experiment?:
1. 
   
2. Unit of measurement
3. Force throwing the paper plane
2. 
   
3. What if we had tried a different design for our second paper airplane AND made it out of construction paper? Could we make the same conclusion?
1. 
   
2. No, because then you would have two independent variables. 

   To brainstorm constant variables, just think:

“  
   Self – Only the independent and dependent variables should change. What do I need to change to keep the same?”

Let’s Try as a Class…

   Think back to Carlos's experiment with the gum. He chewed three different brands of gum and then timed it to see how long the flavor lasted.

    IV: Brand of gum

  
   DV: How long the flavor lasted

   
    Constant Variables:

·      Units of measurement

·      Size of the gum

·      Speed of chewing

Constant Variables and Reliability Lifework

    1) In a complete sentence, describe how you know what the independent variable of an experiment is.

    2) In a complete sentence, describe why a constant variable is important.

3) Name the variables in the experiment below.

Tired of her dirty whiteboard, Ms. Merrifield is trying a new whiteboard cleaner. To see how well it works, she has her students clean one side of the whiteboard with New Brand, and the other side with Old Brand. She then observes how clean each side is.

    

    Independent Variable:_______________________________________________________________________

    

    Dependent Variable:_________________________________________________________________________

    

    Constant Variables:

·       __________________________________________________________________________

·       __________________________________________________________________________

·       __________________________________________________________________________

    4) Mr. Miller is trying to lose weight. He thinks of some things that might help him: eating fewer sweets, running on a treadmill, or taking diet pills. He wants to find out which one is the best quickly, so he tests two things at once – he eats fewer sweets and runs on a treadmill for a week.  Write two-three sentences explaining to Mr. Miller why he will not be able to come to a conclusion this way.