Variable and Control

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Variable and Control

• Which freezes faster
• salt water or fresh water?

2
Experiment

• An organized procedure for testing a hypothesis

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Example of an Experiment

• Will storing microwave popcorn in the freezer
  make it pop better?
• How can this be tested?
• To draw a conclusion, you need a control!

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Control

• A standard for comparison (norm)
• Shows that your result is related to the
  condition you are testing- not to some other
  condition

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Control

• How could you test the popcorn to see if freezing
  the popcorn really does make it pop better?
• What is the control?
• Popcorn stored at room temperature

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Control

• What are the other conditions that need to be
  constant?
• Same brand
• Equally fresh
• Stored for same period of time
• Popped in same microwave oven
• same length of time
• same power

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Constant

• A factor that does not vary in an experiment
• Only one condition should change
• All other factors should remain CONSTANT

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Conclusion

• What happens if one bag were defective?
• How could you be sure that your conclusions were
  accurate?
• REPEAT!!! Store several bags in the freezer and
  several bags at room temperature!

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Variable

• What you are testing

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Independent Variable vs. Dependent Variable
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Home Assignment

• Design and conduct an experiment using material
  that you have at home to answer the question
• Which freezes faster,
• fresh water or salt water?

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Materials

• Use disposable plastic or paper cups
• NOT GLASS
• 1 tablespoon of salt to each ¼ cup of water

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Home Assignment

• Write in your journal
• Problem
• What do you think will happen (Hypothesis)
• What you did (Experiment/Procedure)
• Your observations (Data table)
• Your answer to the question (Conclusion)
• List all constants, 1 variable, 1 control

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Constant

• Type of Cup
• If you put the fresh water in a thin metal cup
  and the salt water in a thick insulated foam cup,
  would that be a fair test? Why or why not?

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Constant

• Type of Cup
• Because the type of cup might affect the
  experiment, do you think you should make sure
  that the cups are the same? How?

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Constant

• Amount of Fresh and Salt Water
• If you used one drop of fresh water and two
  gallons of salt water, would that be a fair test?
  Why or why not?

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Constant

• Amount of Fresh and Salt Water
• Because the amount of water might affect the
  experiment, do you think you should make sure the
  amounts are the same? How?

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Constant

• Temperature of the Fresh and Salt Water
• If the fresh water was 80oC and the salt water
  was only 40oC, would that be a fair test? Why or
  why not?

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Constant

• Temperature of the Fresh and Salt Water
• Because the temperature of the water might affect
  the experiment, do you think you sure the
  temperatures are the same? How?

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Constant

• Temperature of the Freezer
• If you put the freshwater in a freezer set a 0oC
  and the salt water in a freezer set at -15oC,
  would that be a fair test? Why or why not?

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Constant

• Temperature of the Freezer
• Since the temperature of the freezer might affect
  the experiment, do you think you should be sure
  to place the cups in the same freezer? How?

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Variables

• All of the factors that we discussed are called
• VARIABLES!

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Variables

• The idea of a valid, or fair test, is to keep all
  variables constant for both cups, except for the
  one variable you are experimenting with.
• WHAT IS THE VARIABLE IN THIS EXPERIMENT?
• SALT CONTENT!