The scientific method involves designing experiments to test hypotheses. It requires identifying: 1) A change variable that is intentionally altered between trials. 2) A responding variable that is measured to see the effects of the change variable. 3) Control variables that could also influence the responding variable and must be kept constant. Proper experiments only vary one factor at a time to determine causation.

1. SCIENTIFIC
METHOD
Complemented by
my slideshow
Scientific Method
Procedures
By Moira Whitehouse PhD

2. The scientific method is
1. One way scientists find out
about the world around us.
2. Also a procedure scientists
use to answer specific questions.

3. In order to understand the
Scientific Method, we first
need to understand what a
VARIABLE
is

4. A variable is
anything in an experiment
that can change.

5. Here you see a car sitting on top of a ramp.
You want to design a car that will roll down
a ramp really fast.
So you need to know what things affect
how fast a car will roll down a ramp.
What could you change
about this car or ramp
that might affect its
speed?

6. Yes, what could you change or
do to make the car go faster.
These ideas all make up
something we call:

7. variables

8. There are three main kinds of
variables
1. The change variable
2. The responding variable
3. The control variables

9. Let’s look more closely at
these three kinds of variables
Remember the first is called
the change variable.

10. 1. The change variable is:
• There can only be one change
variable in any experiment.
• The variable that the
experimenter changes on
purpose.
• May also be called the
independent variable. (two names for the
same variable)

11. In the experiment on the next
page, identify the change
variable—what is the one thing
the experimenter changed with
plant 1, 2 and 3?

12. Water Water
every every
day day
No Water
20 mL 40 mL
Plant 1 Plant 2 Plant 3

13. Yes, the experiment changed
the amount of water that
the plant receives each day.

14. The second type of variable is
2. The responding variable

15. 2. The responding variable is
• What is measured or observed
by the experimenter to see if
the change variable caused a
different result.

16. The responding variable is
sometimes called the dependent
variable. (again, two names for the same variable)
How this variable responds (goes
faster, grows taller, warms up more, etc.)
depends on the change (or
independent) variable.

17. Let’s look again at the experiment
where the amount of water each
plant received was changed.
What could the experimenter
observe or measure to see if the
amount of water made a
difference to the health of the
plant?

18. Water Water
every every
day day
No Water
20 mL 40 mL
Plant 1 Plant 2 Plant 3

19. The experimenter could have, for
example, counted the number of
green leaves on each plant or he
could have measured the height of
the plants after 14 days.

20. Some examples of responding variables in
different experiments—things to be
observed or measured are:
The amount of water absorbed by two
different brands of paper towels.
How far a ball rolls from different
ramp angles.
The amount of feed eaten at a bird feeder
in response to the type of seed in the
feeder.

21. Whenever possible the experimenter
should measure, instead of just
observing, the responding variable.
In order to measure the responding
variable the experimenter uses tools
such as

22. a metric ruler or meter stick
To measure how far something moved.

23. balance scale
to measure the mass of
something

24. thermometer
To measure how
hot or cold
something is

25. What might the change variable be in this
experiment on water evaporating?
without fan with fan that
moves the air
What could be the responding variable in this
experiment? Remember you should measure.

26. PLASTIC STYROFOAM
CUP OF CUP OF
HOT HOT
WATER WATER
What might the change variable be in this
experiment on keeping water hot?
What might be the responding variable in this
experiment? Remember you should measure.

27. What would the What could be the
change variable responding
be in this variable in this
experiment on experiment?
how much heat Remember you
different soils should measure.
absorb?

28. To use the scientific method to
answer questions, we set up an
experiment that changes just one
thing and then we measure how
that one change affects what we
are interested in.
The question is always “what is
the effect of change variable on
responding variable”?

29. For example, in the case of our
watering plants experiment, the
question might be:
How does the amount of water
you give a plant (change variable)
affect how tall the plant grows.
(responding variable)?

30. But there is more. In every
experiment there is a third
kind of variable called
the control variable.
Control variables are all
those things in an
experiment that you do not
let change.

31. • A control variable is any other
variable (other than the change variable)
that might affect the outcome of
the experiment.
• There may be many control
variables in any experiment
• Control variables must be
kept constant between trials.

32. Think back to our experiment
asking the question: “How does
the amount of water affect how
tall the plant grows in 14 days?”
What variables, other than the
amount of water, could affect
how tall the plant grows?

33. Water Water
every every
day day
No Water
20 mL 40 mL
Plant 1 Plant 2 Plant 3

34. Things that might affect how
tall the plant grows could
include:
1. the amount of light
2. the temperature of the air
3. the kind of soil

35. What would be the problem if
we changed both the amount
of water and the type of soil
the plant is growing in at the
same time?
Sure, you wouldn’t know if the
growth was due to the water or
the type of soil.

36. Water Water
every every
day day
No Water Potting soil
Sandy soil Clay soil
20 mL 40 mL
Plant 1 Plant 2 Plant 3

37. Suppose the plant in the potting
soil that was given 40 mL of
water daily grew the tallest after
14 days?
Could we know whether the 40
mL of water or planting the plant
in potting soil had caused the
results?

38. Probably not: In order to make
correct conclusions when doing
experiments we must:
• have only one change
variable and
• control all other variables
that might affect the results—
keep them constant through out
the experiment.

39. Yes, you would have to plant
all plants in the same potting
soil, use the same kind of
pot, expose all plants to the
same amount of light and
keep the air temperature the
same.

40. So let’s look at that toy car on the
ramp again.
Now, you want to find out if making
the angle of the ramp higher would
make the car coast further.
So your question is:
Will increasing the angle of the
ramp make my car roll further?

41. •What would your change
variable be?
•What would your
responding variable be?
•What would
some of your
control
variables be?

42. Control variables?.
What’s wrong with this
picture? MADE OF PLASTIC
MADE OF
WOOD

43. MADE OF PLASTIC
MADE OF PLASTIC

44. Think you have it! To use the
scientific method to solve a
problem, you set up an
experiment to answer the
question:
What is the affect of the
change variable on the
responding variable?

45. Review
1. Change variable—the thing the
experimenter changes on purpose.
2. Responding variable-- what the
experimenter observes or measures to
see if the change variable is making a
difference.
3. The control variable—the other things
that could cause the responding variable
to change—must be kept the same.