Scientific experiments require carefully controlling variables. The change variable is the only thing that differs between experimental groups. The dependent variable is measured to assess the change variable's effects. Control variables are kept the same in all groups to isolate the independent impact of the change variable. A fair experiment only manipulates one change variable and keeps all else constant.

1. Part 1
SCIENTIFIC
METHOD: Variables
By Moira Whitehouse PhD
Modified by Chele Burch for 5th Grade 8/6/18

2. How do scientists conduct
experiments?

3. Answer: They use the scientific
method.

4. The scientific method is a procedure
scientists use to answer specific
questions.

5. The number 1 purpose of using the
scientific method is to make sure
the experiment is fair.

6. What does a fair experiment look
like? Decide if the following
experiment is fair…

7. Professor William Wonka wonders
if a new formula for plant growth
will make plants grow faster.

8. He decides to grow 2 plants and feed
one of them his special plant food. So,
he buys a hibiscus plant and a bamboo
plant.

9. He measures the height of each plant.

10. He places the hibiscus on a counter in
front of his kitchen window. He places
the bamboo on his bedroom dresser.

11. Every other day, he pours a little water
mixed with his plant food in the hibiscus
plant. And, every other day, he pours a
little water (without the plant food) in
the bamboo plant.

12. After 4 weeks, he measures the height
of each plant again.

13. He observes that the hibiscus plant
grew 2 inches taller, while the bamboo
plant only grew half an inch taller.
2 inches
½ inch

14. So, Professor William Wonka
concludes that his plant food does,
in fact, help plants to grow faster.

15. Is Professor William Wonka correct?
How do you know?

16. Directions: Discuss this question with
your team mates. You may use scratch
paper to help you brainstorm.

17. Is the professor correct? The answer
is….

18. …Not exactly.

19. The professor’s
experiment wasn’t fair.
He can’t be sure that it
was the plant food that
made the hibiscus plant
grow faster than the
bamboo, and not some
other factors.

20. To conduct a fair science experiment,
one must pay attention to the
variables.

21. Consider the following…

22. You want to design a car
that will roll down a ramp
really fast.
ramp

23. So, you need to know what
things affect how fast a car
will roll down a ramp.
ramp

24. What could you do to the car
or ramp to make the car go
faster?
ramp

25. Did you come up with making the
ramp steeper?
How about making the car heavier?
Also, you could grease the wheels to
make them spin more easily.
Can you think of any other things you
could change to make the car faster?

26. All of the things you could change
to make the car go faster are
called...

27. Variables!

28. There are 3 main kinds of
variables:

29. There are 3 main kinds of
variables:
1. The change variable

30. There are 3 main kinds of
variables:
1. The change variable
2. The dependent variable

31. There are 3 main kinds of
variables:
1. The change variable
2. The dependent variable
3. The control variables

32. Let’s look more closely at
these 3 kinds of variables.

33. The 1st type of variable is:
1. The change variable

34. 1. The change variable is:
• the only thing in the experiment
that isn’t kept the same.
• also known as the independent
variable.

35. Important!!!
• There can only be 1 change
variable in any experiment!!!!

36. In the experiment on the next
slide, identify the change
variable.
What is the 1 thing that isn’t the
same with plant 1, 2, and 3?

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

38. You are correct if you said the
change variable is the amount
of water each plant receives.

39. The 2nd type of variable is:
2. The dependent variable

40. 2. The dependent variable is
• What you measure or observe
to see how the change
variable affects the
experiment.

41. In our 3 plants/water
experiment, what could be
some dependent variables?
(What could the experimenter observe or
measure to see if the amount of water
made a difference to the health of each
plant?)

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

43. The experimenter could have, for
example, counted the number of
green leaves on each plant. So, the
number of leaves is a dependent
variable.

44. He could also have measured the
height of the plants after 14 days.
So, plant height could be another
dependent variable.

45. Here are some examples of
dependent variables in other
experiments:

46. Dependent Variable:
...the amount of water absorbed by
two different brands of paper towels...

47. Dependent Variable:
...how far a ball rolls from different
ramp angles...

48. Dependent Variable:
...and the amount of bird food eaten at
a bird feeder when the type of bird
food is changed.

49. Whenever possible the experimenter
should measure, instead of just
observe, the dependent variable.

50. In order to measure the dependent
variable, the experimenter uses tools
such as...

51. ...a metric ruler or meter stick
to measure how far something
moved...

52. ...a balance scale to measure
the mass of something...

53. ...and a thermometer to
measure how hot or cold
something is.

54. What might the change variable be in
this experiment on water evaporating?
without fan with fan that
moves the air

55. What could be the dependent variable
in this experiment? Remember you
should measure.
without fan with fan that
moves the air

56. What might the change variable be in
this experiment on keeping water hot?
PLASTIC
CUP OF
HOT
WATER
STYROFOAM
CUP OF
HOT
WATER

57. What might be the dependent variable
in this experiment? Remember you
should measure.
PLASTIC
CUP OF
HOT
WATER
STYROFOAM
CUP OF
HOT
WATER

58. What would the
change variable
be in this
experiment on
how much heat
different soils
absorb?

59. What could be the
dependent variable
in this experiment?
Remember, you
should measure.

60. Now, you have an understanding of
what a change variable and
dependent variable are, but there
is 1 more type of variable...

61. The 3rd type of variable is
3. The control variables

62. Control variables are all those
things in an experiment that you
keep the same.

63. Unlike a change variable, there can
be many control variables in an
experiment.

64. Think back to our experiment
with the 3 plants and amount of
water.
What are the control variables?
(What should be kept the same?)

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

66. The control variables could
include:
1. the amount of sunlight
2. the temperature of the air
3. the kind of soil
4. the size of the pot

67. 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?

68. Answer: You wouldn’t know if the
growth was due to the water or the
type of soil.

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

70. Let’s review…

71. In order to make correct conclusions
when doing experiments we must:
• have only ONE change variable.
• keep EVERYTHING else the same.

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

73. •What would your
change variable be?

74. •What would your
dependent variable
be?

75. •What would some
of your control
variables be?

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

77. MADE OF PLASTIC
MADE OF PLASTIC

78. 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 dependent
variable?

79. What is a change variable?

80. What is a change variable?
A change variable is the only thing
that is different in an experiment.

81. What is a dependent variable?

82. What is a dependent variable?
A dependent variable is what you
measure or observe to determine
how the change variable affected
the experiment.

83. What are control variables?

84. What are control variables?
Control variables are the things
that must be kept the same.

85. Good job!

86. On the left side page of your
science notebook, create a one-
pager that demonstrates what you
know about change variables,
dependent variables, and control
variables. You will be graded on
this.