Variables in Science Experiments

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Variables in Science Experiments

• What makes an experiment fair?

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Variables

• A variable is something that is changed
• A constant, or control, is something that does
  not change

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Science experiments use

• Independent Variable the one factor that is
  changed by the person doing the experiment
• Dependent Variable the factor which is measured
  in the experiment
• Constants all the factors that stay the same in
  an experiment

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A birdy example

• Imagine you want to see what color of bird
  feeders your local birds preferred.
• Red? Blue? Green?

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Our Constants and Variables

• Independent Variable color of the feeders
• Dependent Variable amount of seed eaten
• Constants everything else that is kept the same,
  for example
• the location of the feeders
• the kind of feeder used
• putting the feeders out at the same time

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Our Experimental Design
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If everything except the independent variable is
held constant, we can say

• The experiment is FAIR.
• (ONLY the independent variable can change!)

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Why is it important to only change the
independent variable?
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If you dont

• If you measure a change in the dependent
  variable, you wont know whether it is the
  independent variable that is causing the change.

Independent Variable
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Is Sams experiment fair? YES? NO?

• NO! It isnt fair since the locations of the
  feeders were very different!

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Is Marias experiment fair?YES? NO?

• YES! It seems fair since Maria only changed the
  feeder color!

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Is Jessies experiment fair?YES? NO?

• NO! It isnt fair since the feeders are not out
  at the same time, and we know that the weather
  was quite different each time. Perhaps the
  number and kind of birds that visited during the
  weeks were different due to the weather.

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What do you think?

• Terry loves birds and wants to see as many as she
  can in her yard. She wants to know whether she
  is wasting money buying an expensive mixed seed,
  when a cheaper brand just arrived at her local
  store. She wonders will the expensive seed
  attract more birds to her back yard?

How would you advise her to find out if the
expensive seed is better?
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Terrys Experimental Design
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Terrys Experimental Design

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What experiments are you planning?

• What are your variables?
• How will you keep your experiment fair?