Designing an Investigation

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Designing an Investigation
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In an investigation we change one variable and
see how it affects another variable
The independent variable the variable that we
change The dependant variable the variable
that changes as a result
In most investigations there will be a choice of
which variable to change and which to measure
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A students measures how quickly a reaction
between acid and metal happens by counting the
number of bubble produced in a minute. They do
this for several different metals.

• What is
• The independent variable in this experiment?
• The dependant variable?
• Another independent variable they might have
  chosen?
• Another dependant variable they might have chosen?

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A Fair Test
The change in the dependant variable should be
due to the change that we made in the independent
variable. NOT because another variable
changed. Other variables should be controlled,
kept the same.
What affects how many tomatoes a plant produces?
Height of the plant
Amount of water
Type of plant
Type of soil
Temperature
Amount of sunlight
Number of leaves
Age of plant
Nutrients given
Size of pot
If we want to investigate any of these we should
try to control all the others in our experiment.
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Sometimes it is difficult to control variables,
e.g. in the field.
We cant control the weather but at least we know
it will be the same for all of these trees.