Year 7 Variables: Independent, Dependent, Controlled
A variable is part of an experiment that can change, such as amount of light, temperature, humidity, time
changes, or plant growth.
Independent Variable
In an experiment, an independent variable is a variable that either changes on its own, or you purposely
change it.
For example: If the purpose of an experiment is to determine how changes in the amount of light on a plant
affects the plant’s growth.
How Plants Grow In Response to Light
The Independent Variable is the amount of light the plant received.
Ideas for how to change the amount of light.
1. Use sunlight which changes during the day as well as from one day to the next.
You can also use direct and indirect sunlight.
2. If you use artificial light you can determine when and for how long the plant will receive this light. You
also have the option to control the wattage of light used–its colour–type (fluorescent, UV, incandescent).
Just use the same type of light for each test plant–see controlled variables below.
Dependent Variable
The purpose of changing an independent variable is to determine how the changes affects something else,
which is called the dependent variable. In other words, changes in the independent variable may cause the
dependent variable to change.
In an experiment, a dependent variable may change due to the changes made in the independent variable.
For the previous plant experiment, “How Plants Grow In Response to Light,” the growth of the plant is the
dependent variable being observed. The plant growth is in response to changes in the amount of light the
plant receives, is the independent variable.
Controlled Variables
Controlled variables sounds like an oxymoron. Just remember that variables are things that CAN change.
This means that they can be controlled and prevented from being changed.
It is important that when you experiment that you have only two variables that change:
1. the independent variable that you want to change and can measure how it changes.
2. the dependent variable that you are measuring to see how much it changes in response to the independent
variable.
Changes in any other variable could affect your results. So, you must try to control any other variable,
meaning you want to eliminate them or control them so that the things being tested are not affected.
For example, in the previous experiment, “How Plants Grow In Response to Light,” the variables that must
be controlled include, the type of plant tested, container, type of soil, temperature, amount of water,
humidity, type of light, etc…needs to be the same for every plant tested. Some variable are difficult to
control, but you should try to make every effort to keep them the same during the testing.
Identify the Controls and Variables
Smithers thinks that a
special juice will increase
the productivity of workers.
He creates two groups of 50
workers each and assigns
each group the same task (in
this case, they're supposed to staple a set of
papers). Group A is given the special juice to
drink while they work. Group B is not given the
special juice. After an hour, Smithers counts how
many stacks of papers each group has made.
Group A made 1,587 stacks, Group B made 2,113
stacks.
Identify the:
1. Control Group
2. Independent Variable
3. Dependent Variable
4. What should Smithers'
conclusion be?
5. How could this experiment be
improved?
Homer notices that his
shower is covered in a
strange green slime. His
friend Barney tells him that
coconut juice will get rid of
the green slime. Homer
decides to check this this out
by spraying half of the
shower with coconut juice. He sprays the other
half of the shower with water. After 3 days of
"treatment" there is no change in the appearance
of the green slime on either side of the shower.
6. What was the iniitial
observation?
Identify the7. Control Group
8. Independent Variable
9. Dependent Variable
10. What should Homer's
conclusion be? It doesn't work
Bart believes that mice exposed to radiowaves will
become extra strong (maybe
he's been reading too much
Radioactive Man). He decides
to perform this experiment by
placing 10 mice near a radio for
5 hours. He compared these 10
mice to another 10 mice that
had not been exposed. His test
consisted of a heavy block of wood that blocked
the mouse food. he found that 8 out of 10 of the
radiowaved mice were able to push the block
away. 7 out of 10 of the other mice were able to do
the same.
Identify the11. Control Group
Krusty was told that a certain
itching powder was the newest
best thing on the market, it even
claims to cause 50% longer lasting
itches. Interested in this product,
he buys the itching powder and
compares it to his usual product.
One test subject (A) is sprinkled
with the original itching powder, and another test
subject (B) was sprinkled with the Experimental
itching powder. Subject A reported having itches
for 30 minutes. Subject B reported to have itches
for 45 minutes.
Identify the16. Control Group
Lisa is working on a science
project. Her task is to answer the
question: "Does Rogooti (which is
a commercial hair product) affect
the speed of hair growth". Her
family is willing to volunteer for
the experiment.
20. Describe how Lisa would
perform this experiment. Identify
the control group, and the
independent and dependent
variables in your description.
12. Independent Variable
13. Dependent Variable
14. What should Bart's conclusion
be?
15. How could Bart's experiment
be improved?
17. Independent Variable
18. Dependent Variable
19. Explain whether the data
supports the advertisements claims
about its product.