3. Before we can perform an experiment
designed to answer this question, we must
determine the independent and dependent
variable.
For an experiment to have valid results, there
can be only one independent variable.
THIS IS IMPORTANT!

4. The independent variable is the variable
that you, as the scientist, will vary to
observe the effect
The independent variable is sometimes
called the manipulated variable because it is
the variable the scientist manipulates.

5. The dependent variable is the variable that
you, as the scientist, will measure and
record – it’s the data of the experiment
The dependent variable is sometimes called
the “responding” variable because it is the
variable that responds to the independent
(or manipulated) variable

6. To determine the independent and dependent
variable, identify the two things that will
(might) change:
lack of sleep
weight of an individual

7. Once you know the two things that are (or might be)
changing, arrange them in a question like this:
In this experiment, does the lack of sleep depend on
weight gain?
OR
Does weight gain depend on lack of sleep?
The variable that depends on the other is the
dependent variable.

8. A lack of sleep depends on weight gain?
OR
that weight gain depends on a lack of sleep?
Weight gain depends on the lack of sleep so
weight gain is the dependent variable.

9. It’s important to understand that you don’t
yet have to know if weight gain depends on
a lack of sleep – you just need to identify
which variable you will be manipulating and
which variable will respond to your
manipulations.

10. What effect does being raised on a fish farm
have on a salmon’s length?
What two factors are being studied?
salmon’s length
raised on a fish farm

11. What effect does being raised on a fish farm
have on a salmon’s length?
Does being raised on a fish farm depend on
the salmon’s length?
OR
Does the length of the salmon depend on
being raised on a fish farm?

12. The length of the salmon depends on being
raised on a fish farm
Independent Variable?
raised on fish farm
Dependent Variable?
length of salmon

13. On the following slides, write down the
research question in your notes and then
discuss with your partner what you believe
the two factors that will (might) change are.
After you agree on the two factors, see if you
can agree on which one is the independent
variable and which one is the dependent
variable.

14. Two factors being studied?
presence of music
number of tomatoes grown

15. presence of music number of
tomatoes
dependent variable?

16. Two factors being studied?
frequency of exercise
number of infections with cold virus

17. exercise number of colds
over a specified
time period
dependent variable?

18. Two factors being studied?
use of cell phones while driving
number of automobile accidents
involved in

19. use of cell phones
while driving
number of auto
accidents involved
in
dependent variable?

20. Once you know the independent and
dependent variables, writing a hypothesis
statement is easy!
A hypothesis simply combines the
independent and dependent variables into a
prediction statement.

21. Research Question: What effect does salt have
on the boiling point of water?
Independent Variable:
adding salt
Dependent Variable:
boiling point of water

22. IV: adding salt to H2ODV: boiling temp
A good hypothesis statement is an “if” “then”
statement.
If salt is added to water, then the boiling point
of water will increase.

23. If salt is added to water, then the boiling point
of water will increase.
The independent variable is the “if” part of the
hypothesis and the dependent variable is the
“then” part.

24. a statement that predicts something
testable
an “if” “then” statement

25. a question
a statement that has words in it like
maybe
probably
might

26. A hypothesis might also have a “because”
section
In the prior example, the “because” would
sound like this:
If salt is added to water, then the boiling
point will increase because salt is an ionic
compound and ionic compounds are known
to elevate boiling points.

27. What is the effect of wing size on the falling
speed of a rotocopter?
What are the two factors?
wing size
falling speed
Which factor is the independent variable?
Dependent variable?
ind v: wing size dep v: falling speed

28. ind v: wing size dep v: falling speed
If the wing size is increased, then the falling
speed of the rotocopter will decrease.
or
If the wing size is increased, then the falling
speed of the rotocopter will decrease
because increased wing size will result in
increased air resistance.

29. What effect does sandpaper have on a block
of wood’s sliding velocity?
Two factors?
sandpaper
sliding velocity
Ind V and Dep V?
IV: sandpaper DV: sliding velocity

30. IV: sandpaper DV: sliding velocity
If a block of wood is pulled on a sandpaper
surface instead of a wooden surface, then the
sliding velocity will decrease.
or
If a block of wood is pulled on a sandpaper
surface instead of a wooden surface, then the
sliding velocity will decrease because the force
of friction of the sandpaper will be greater.

31.  THE FINE PRINT
 © Jan Parker, 2009 – for purchaser’s classroom use only; please do not distribute. If other teachers in your school like
what they see, send them to my website http://www.thesciencevault.com or to my web store
http://www.teacherspayteachers.com/Store/Jan-Parker 
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