Variables

1
Variables

• Designing a fair experiment

2
What is a Variable?

• Scientists design experiments in which changes to
  one item cause something else to change in a
  predictable way.
• A variable is any factor, trait, or condition
  that can exist in differing amounts or types. An
  experiment usually has three kinds of variables
• Controlled
• Independent
• Dependent

3
Independent Variables

• The independent variable is purposefully changed
  by the scientist
• A good, fair test only has one independent
  variable
• Why is it important to only have one independent
  variable?

4
Dependent Variables

• The dependent variable is caused by and depends
  on the independent variable.
• The scientist focuses his/her observations on how
  the dependent variable changes in response to the
  independent variable.
• Why is it necessary to observe the dependent
  variables?

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Example

• The longer the amount of time spent studying
  causes an increase in test scores
• Remember independent variable is changed
  purposefully and the dependent variable changes
  in response

• Independent Variable time spent studying
• Dependent Variable test scores

6
Controlled Variables

• Controlled variables are values that a scientist
  wants to remain constant
• They must be observed as closely as the dependent
  variables in order to maintain a fair test
• There is usually more that one controlled
  variable
• Controlled variables are also known as constant
  variables
• Why does an experiment need controlled variables?

7
Variables

• In a good experiment, the independent and
  dependent variables are both measurable.
• Time, mass, length are all examples of measurable
  values
• Variables with no true unit of measure would be a
  poor variable to use in an experiment (i.e.
  love, success)?

8
More Examples
9
Your turn.

• After studying about recycling, members of Johns
  Biology class investigated the effect of various
  recycled products on plant growth. Johns lab
  group compared the effect of different aged grass
  compost on bean plants. Each plant received the
  same amount of sunlight and water each day.
• Identify the controlled, independent and
  dependent variables.

10
Answers

• Independent Variable
• Amount of compost
• Dependent Variable
• Height of bean plant

• Controlled Variables
• Amount of sunlight
• Amount of water

11
The Role of Variables in the Scientific Method

• Variables play an important part in the
  scientific method.
• A hypothesis is formatted according to the
  independent and dependent variables.
• A graph (data analysis) is labeled according to
  the independent and dependent variables
• Variables are further explained in the
  conclusion.

12
Hypothesis

• A hypothesis is a possible answer to a scientific
  question. It is NOT an educated guess.
• A hypothesis should always be presented in the
  form of an If.then.. statement.
• If is followed by the independent variable,
  then is followed by the dependent variable.
• Example - If a plant is grown in compost, then it
  will grow taller.

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Hypothesis Practice

• Independent Variable time spent
  studying Dependent Variable test grade
• Independent Variable light or dark Dependent
  Variable - of earthworms
• Independent Variable fertilizer Dependent
  Variable height of plant