VARIABLES
HYPOTHESIS
AIM
CONCLUSION
THE SCIENTIFIC METHOD
WHAT ARE
VARIABLES?
• Scientists try to figure out how the
natural world works. In doing so,
they use experiments to search
for cause and effect relationships.
• Cause and effect relationships
explain why things happen and
allow you to reliably predict what
will happen if you do something. In
other words, scientists design an
experiment so that they can
observe or measure if changes to
one thing cause something else to
vary in a repeatable way.
WHAT ARE
VARIABLES?
• The things that are changing in an
experiment are called variables.
• A variable is any factor, trait, or
condition that can exist in differing
amounts or types.
• Simply put, a variable is anything
you can change or control in an
experiment.
• Examples: temperature, duration of
the experiment, composition of a
material, amount of light
TYPES OF
VARIABLES
• There are three kinds of
variables in an experiment
• Independent variables or
manipulated variables
• Dependent or responding
variables
• Controlled variables
Manipulated or
Independent
variable
is the one factor that you
are changing.
➢It is only one factor
because usually in an
experiment you try to
change one thing at a
time.
WHY ONLY ONE FACTOR IS
CHANGED?
WHY ONLY ONE
FACTOR IS
CHANGED?
❑This makes measurements
and interpretation of the
data much easier.
❑ if you changed more than
one variable it would be
hard to figure out which
change is causing what you
observe.
What is the
manipulated
variable?
❑If you are trying to determine
whether heating water
allows you to dissolve more
sugar in the water then your
manipulated variable is the
…................................................
...................................................
What is the
manipulated
variable?
❑If you are trying to determine
whether heating water
allows you to dissolve more
sugar in the water then your
manipulated variable is the
temperature of the water
Responding or
dependent
variable
❑are the things that the
scientist focuses his or her
observations on to see how
they respond to the change
made to the manipulated
variable.
❑the variable you observe, to
see whether it is affected by
your manipulated variable.
What is the
responding
variable?
❑If you are trying to determine
whether heating water
allows you to dissolve more
sugar in the water then your
responding variable is the
…................................................
...................................................
What is the
responding
variable?
❑If you are trying to determine
whether heating water
allows you to dissolve more
sugar in the water then your
responding variable is the
mass or volume of sugar
(whichever you choose to
measure)
Controlled
variables
❑Controlled variables, sometimes
called constant variables are
variables that are kept constant
or unchanging.
❑Example, . If you are performing
an experiment on the effect of
spraying plants with different
chemicals, you would try to
maintain the same pressure and
maybe the same volume when
spraying your plants.
What are the
controlled
variables?
❑If you are trying to determine
whether heating water
allows you to dissolve more
sugar in the water then your
controlled variables are
……………………………………………………
……………………………………………………
…………………………………………………….
What are the
controlled
variables?
❑If you are trying to determine
whether heating water
allows you to dissolve more
sugar in the water then your
controlled variables are
✓ volume of water used
✓ number of times stirred
✓ length of time for stirring
EXAMPLE:
Question
Manipulated
Variable
(What I
change)
Time
How fast does
measured, in
a candle burn?
minutes
Responding
Variable
(What I
observe)
Controlled
Variables
(What I keep
the same)
Height of
candle,
measured in
centimeters, at
regular
intervals of time
(for example,
every 5
minutes)
•Use same type
of candle for
every test
•Wind—make
sure there is
none
Making a hypothesis
• A hypothesis is a statement, not a question
• A hypothesis (plural: hypotheses) is an
educated, testable prediction about what
will happen.
• Like all predictions, hypotheses are based on
a person’s observations and previous
knowledge or experience.
• In science, a useful hypothesis is a testable,
measurable statement which may include a
prediction.
Making a hypothesis
• A GOOD HYPOTHESIS SHOULD
1: The “IF” / “THEN” statement form of hypothesis
• Parts of the Statement
• Manipulated Variable:
• The condition be studied. It is controlled
by the experimenter e.g temperature
• Responding Variable:
• The condition affected by the
manipulated variable.
• Start your sentence with the word
“If”
• Write down the manipulated
variable
Connect statement with one of the
following:
is related to
is affected by
causes
• Write down the other responding
variable
• Writing the “Then” section of your
Hypothesis
• Write the word then (following the “if”
section)
• Make a comment on the relationship
between those two variables.
• EXAMPLE: If section: If water is related to
plant growth,
• EXAMPLE:. Then section: then the more
you water plants, the bigger they will
grow.
MAKE A HYPOTHESIS USING
“IF/THEN”
The cooler the temperature in a lake, the
more oxygen the water holds. Daniel
notices that he catches more fish in a
lake that is cooler than 55 degrees. He
wants to conduct a study so he can catch
the most fish possible this year. He’s
having trouble writing a hypothesis.
Please help him.
MAKE A HYPOTHESIS USING
“IF/THEN”
Hypothesis:
If temperature of water is
related solubility of oxygen in
water then cold waters will
hold more oxygen than warm
waters and will have more fish
2: The choice hypothesis
Useful when investigating the
preferences of an organism
Given a choice “THE” will
“PREFER” than “OTHER
PREFERENCE” statement.
Example: Snails prefer wet soil
to dry soil
• The cooler the temperature in
a lake, the more oxygen the
water holds. Daniel notices
that he catches more fish in a
lake that is cooler than 55
degrees. He wants to conduct
a study so he can catch the
most fish possible this year.
He’s having trouble writing a
hypothesis. Please help him.
• Now rewrite your last
hypothesis as a choice
hypothesis
Fish prefer cold waters to
warm waters
3. Observational hypothesis
Useful when studying organisms
in the field and when conditions
cannot be changed; can also
be a comparative statement.
“ORGANISM X” is “STATEMENT
ABOUT DISTRIBUTION, DENSITY”,
and “SIZE ETC”.
Example: More pyrethrum is
grown in cool temperate
regions than in hot regions
• Suppose you and your
neighbour are growing
tomatoes. One day you
notice that your neighbour’s
plants are much bigger than
yours. What’s causing the
difference?
• How can you get your plants
to grow as big as your
neighbour’s?
• MAKE AN OBSERVATIONAL
HYPOTHESIS
Watering plants makes
them grow taller
Temperat
ure/C
0
15
30
45
60
70
Amount
sugar
/arbitrary
units
12
40
70
90
30
3
The results shown in Table 1 are obtained when
samples of starch suspension are mixed with saliva
and left in water baths at different temperatures for
20 minutes.
1. Identify the manipulated variable
2. Identify the responding variable
3. Identify two controlled variables
4. Write a likely hypothesis for this experiment
Writing an AIM
• An aim is a single statement that describe the purpose or
reason for why we are conducting an experiment.
• An aim should be brief and concise.
• It should state the purpose of the experiment without
providing a prediction. An aim usually starts with "To
determine...“ or “To observe….”
•
WRITE AN AIM
• “Ashley plants three seedlings in pots. She places each plant in
a different spot in the classroom depending on sunlight. She
place the first plant on the window sill where the sun shines all
through the day; she places the second plant on the table at
the front of the class where the sun only shines half the day;
she places the last plant in the cupboard where it gets no light.
She waters the plants equally and leaves them to grow for a
week measuring how tall they get."
What is the aim of Ashley's experiment?
Writing a conclusion
• Check your results first
• The best place to start when writing the conclusion is to go
back to the aim. Read it again and see what the
experiment was trying to show. Did it show that or
something totally different?
• If a hypothesis was given in the aim, the conclusion should
state whether the hypothesis was confirmed or
contradicted by the experiment.