1. Designing an Experiment
I. Determining a Purpose
An experiment is an organized procedure to study something under controlled conditions.
Write the purpose of your experiment as a question or
problem you want to investigate

2. Investigating a Problem
To design an experiment, you need a purpose for the experiment.
The purpose is the question you wish to investigate. The question
should be written so that it cannot be answered with
a “yes” or a “no”.
Observation:
You notice that the rocks in the middle of the river have rounded
edges. On the edge of the river, the rocks have sharper edges.
Question:
Why are the rocks in the middle of the river more rounded
than those on the edges?

3. Observation:
You put a plant on a windowsill. After a few weeks, you notice
that the leaves have all turned toward the window.
Question:
Why do the leaves of a plant turn toward the window?
Observation:
You notice that when you eat chocolate ice cream at night, you have trouble falling asleep.
Question:
Is there something in chocolate ice cream that keeps me awake
at night?

4. Does increasing the air in a basketball make it bounce higher?
You observe when playing basketball that sometimes the ball bounces higher. Later, while filling the basketballs with air you notice that the amount of air in the basketballs can be different.
Question:
Does increasing the air in a basketball
make it bounce higher?
Prediction:
Increasing the air in a basketball will/will not make it bounce
higher.
Observation #1

5. Cars on higher ramps will/will not travel farther.
While watching your brother play with his toy cars, you notice when
he rolls them down a ramp that they travel different distances. You
wonder if the height of the ramp has any affect on how far the
cars travel.
Question:
Will increasing the height of a ramp cause a car to travel farther?
Prediction:
Cars on higher ramps will/will not travel farther.
Observation #2 5

6. Will soaking seeds in water affect sprouting time? Prediction:
Question:
Will soaking seeds in water affect sprouting time?
Prediction:
Seeds soaked in water will sprout faster.
Question:
2. Will freezing popcorn affect the amount of kernels that pop?
Prediction:
Freezing popcorn will cause more kernels to pop.
Question:
3. Will increasing the temperature of water affect the amount of time
it takes sugar to dissolve?
Prediction:
Increasing the temperature of water will cause sugar to dissolve
faster.
Packet p.3

7. 4. Does the temperature at which bread is stored affect mold growth?
Question:
4. Does the temperature at which bread is stored affect mold growth?
Prediction:
Storing bread at cooler temperatures will cause mold to grow more slowly.
Question:
5. Does water temperature affect the time it takes water to freeze?
Prediction:
Increasing water temperature will cause water to freeze more quickly.
Packet p.3

8. II. Writing a Hypothesis
A hypothesis is a tentative explanation for an observation or scientific problem that can be tested by further investigation.
A hypothesis is written in the form of an if/then
statement.

9. You observe when playing basketball that sometimes the ball bounces
higher. Later, while filling the basketballs with air you notice that the
amount of air in the basketballs can be different.
Question:
Does increasing the air in a basketball
make it bounce higher?
Prediction:
Increasing the air in a basketball will/will not make it bounce
higher.
Hypothesis:
If the amount of air in a basketball is increased,
then it will bounce higher.
Observation #1
p. 4 9

10. Cars on higher ramps will/will not travel farther.
While watching your brother play with his toy cars, you notice when he rolls them down a ramp that they travel different distances. You wonder if the height of the ramp has any affect on how far the cars travel.
Question:
Will increasing the height of a ramp cause a car to travel farther?
Prediction:
Cars on higher ramps will/will not travel farther.
Hypothesis:
If the height of a ramp is increased, then a car will travel farther.
Observation #2
p. 4 10

11. Will soaking seeds in water affect sprouting time?
Hypothesis:
If seeds are soaked in water, then seeds will sprout faster.
2. Will freezing popcorn affect the amount of kernels that pop?
Hypothesis:
If popcorn is frozen, then more kernels will pop.
3. Will increasing the temperature of water affect the amount of time
it takes sugar to dissolve?
Hypothesis:
If the temperature of water is increased, then sugar
will dissolve more quickly.
Packet p.5

12. 4. Does the temperature at which bread is stored affect mold growth?
Hypothesis:
If bread is stored at a cooler temperature, then mold
will grow more slowly.
5. Does water temperature affect the time it takes water to freeze?
Hypothesis:
If water temperature is decreased, then water
will freeze more quickly.
Packet p.5

13. III. Determining Variables and Constants
a. Variables and Constants
i. A variable is any factor in an experiment that can change.
ii. Constants are all of the factors that are the same.
iii. The independent variable is the factor you want to test.
An independent variable is expressed in your hypothesis
after the word “If”.
v. The dependent variable is the factor that you measure to
get your results.
A dependent variable is expressed in your hypothesis after
the word “then”.

14. Hypothesis #1 : If the amount of air in a basketball is
increased, then it will bounce higher.
Independent variable:
amount of air
Dependent variable:
height of bounce
Hypothesis #2: If the height of a ramp is increased, then a car will
travel farther.
Independent variable:
ramp height
Dependent variable:
distance traveled

15. percent of kernels popped
If seeds are soaked in water, then seeds will sprout faster.
Independent variable:
Dependent variable:
2. If popcorn is frozen, then more kernels will pop.
3. If the temperature of water is increased, then sugar will dissolve more quickly.
soaking seeds
sprouting time
freezing popcorn
percent of kernels popped
water temperature
dissolving time

16. time it takes mold to grow
4. If bread is stored at a cooler temperature, then mold will grow more slowly.
Independent variable:
Dependent variable:
5. If water temperature is decreased, then the water will freeze more quickly.
storing temperature
time it takes mold to grow
water temperature
freezing time

17. b. Measuring the Dependent Variable
i. An operational definition is a description of the particular way in
which you will measure the dependent variable.
ii. Operational definitions can be qualitative or quantitative.

18. Defining Variables Operationally
Hypothesis:
If students have more lunch money,
then they will eat a poorer quality diet.
Hypothesis:
If students spend more time studying each week,
then they will do better in school.
Hypothesis:
If fertilizer is added to tomato plants,
then they will grow better.

19. Identifying Variables
1. What variables can affect the rate at which seeds sprout?
soaking seeds
temperature
sunlight
type of seed
soil
What variables can affect the number of popcorn kernels that pop?
freezing
type of popcorn
popping time
microwave
popcorn brand

20. 3. What variables can affect the dissolving rate of sugar in water?
water temperature
type of sugar
amount of sugar
amount of water
stirring
4. What variables can affect mold growth on bread?
storing temperature
type of bread
storage container
amount of sunlight/darkness
moisture in bread

21. 5. What variables can affect the time it takes water to freeze?
water temperature
container
amount of water
freezer
location and temperature in freezer 21

22. Controlling Variables
Hypothesis #1 : If the amount of air in a basketball is
increased, then it will bounce higher.
Independent variable:
Dependent variable:
amount of air
height of bounce
The constants are all the factors that are the same.
same basketball
same temperature
same surface
same bounce height
Packet page 8

23. Independent variable:
Hypothesis #2: If the height of a ramp is increased, then a car will
travel farther.
Independent variable:
Dependent variable:
ramp height
distance traveled
Constants:
same surface
same car
same ramp

24. Example #1
Hypothesis: If seeds are soaked in water, then they will sprout faster.
Independent variable:
soaked seeds
Dependent variable:
sprouting time
Constants:

25. Example #2
Hypothesis: If popcorn is frozen, then more kernels will pop.
Independent variable:
freezing kernels
Dependent variable:
percentage of popped kernels
Constants

26. Independent variable:
Example #3
Hypothesis: If the temperature of water is increased, then sugar
will dissolve more quickly.
Independent variable:
water temperature
Dependent variable:
dissolving time
Constants

27. Independent variable:
Example #4
Hypothesis: If bread is stored at a cooler temperature, then mold will
grow more slowly.
Independent variable:
storing temperature
Dependent variable:
mold growth
Constants

28. Example #5
Hypothesis: If water is decreased then freezing time will decrease.
Independent variable:
water temperature
Dependent variable:
time it takes to freeze
Constants 28

29. Independent variable:
Experiment #1
Mr. Hunsicker has observed that the batteries in his boom box seem
to last longer if he plays his boom box at low volume rather than high
volume. He wants to design an experiment to determine if this is true.
If a boom box is played at low volume, then the batteries will last longer.
Independent variable:
boom box volume
Dependent variable:
battery life
Constants:
boom box
batteries CD

30. number of daylight hours henhouse-climate/temperature
Experiment #2
An investigator has observed that chickens lay more eggs at certain times of
the year. It has also been observed that this occurs during the late spring
and summer months. An inference has been made that the extra eggs are
due to the longer daylight hours.
If the number of daylight hours is greater, then chickens will lay more eggs.
Independent variable:
number of daylight hours
Dependent variable:
number of eggs laid
Constants:
chickens
henhouse-climate/temperature
diet/water

31. type of street traveled gas mileage car driver type of gas
Experiment #3
Johnny made an observation that when he drove around the city on the
highway to work everyday, he did not have to get gas as often as when
he drove through the city. He then asked himself Do the type of roads I
drive to work on everyday affect my gas mileage?
If cars are driven on the highway, then gas mileage will increase.
Independent variable:
type of street traveled
Dependent variable:
gas mileage
Constants:
car
driver
type of gas

32. If bread is moist, then mold will grow faster.
Experiment #4
Troy wanted to determine if mold grows faster on moist bread or dry bread.
He placed one piece of bread in a dry baggie and another piece of bread
in a damp baggie. He checked them every eight hours and recorded
his observations.
If bread is moist, then mold will grow faster.
Independent variable:
moisture on bread
Dependent variable:
mold growth
Constants:
bread
temperature
sunlight

33. different types of drinks
Experiment #5
Hannah wanted to test the ability of different drinks to dissolve bones. She filled glass jars with orange juice, milk, cola, and distilled water. Hannah
then placed a chicken bone in each of the jars.
Independent variable:
different types of drinks
Dependent variable:
dissolving of bone
Constants:
bones – size and type
amount of liquid
temperature

34. percent of kernels popped
Experiment #6
Sarah wanted to determine which of three brands of popcorn popped the most kernels. She put one brand in the microwave, set the timer for four minutes, and allowed the bag to pop. She repeated this process for each bag.
Independent variable:
brand of popcorn
Dependent variable:
percent of kernels popped
Constants:
microwave
time
type of popcorn

35. Summarizing Results
When summarizing your data, look at all of your observations,
Then look for meaningful ways to present your observations.

36. Data Tables
Growth Rate of a Child
Age (years)
Weight (kg)

37. Graphs Line graphs are useful for showing changes over time.
The dependent variable
is placed along the
y-axis.
The independent variable is placed
along the x-axis.

38. Bar graphs are useful for comparing data.
The dependent variable
is placed along the
y-axis.
The independent variable is placed
along the x-axis.

39. Birth 1 year 2 years 3 years 4 years 5 years
Growth Rate of a Child . 20 18 16 14 12 10 8 6 4 2 . . .
Weight (kg) . .
Birth year years years years years
Age (years)