The Scientific Method
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An experiment tests an idea in a
careful orderly manner. The
orderly steps used are called
The Scientific Method.
Stating the Problem
• A scientific question
that can be answered
by gathering evidence.
Example:
Which freezes
faster, fresh water
of salt water?
Research
Gathering information on the problem.
Develop a Hypothesis
• A hypothesis is a
prediction about the
outcome of the
experiment. A
properly worded
hypothesis should take
the form of an If
…then… statement.
Example:
If I add salt to
fresh water, then
the water will
take longer to
freeze.
Designing an Experiment
• Next, you need to develop
a plan to test your
hypothesis. Your plan
should describe the
observations or
measurements you will
make.
• In a well designed
experiment, you need to
keep all variables the same
except for one.
•
•
•
•
A variable is any factor that can
change in an experiment.
The factor that you change is
called the manipulated
variable or independent
variable.
The responding variable or
dependent variable is what you
measure or observe to obtain
your results.
A controlled variable is a
factor that is kept constant. You
use the control to make a
comparison.
Example of an
Experimental Procedure
Fill 3 containers with
•
300 milliliters of cold tap
water.
2. Add 10 grams of salt to
•
container 1 and stir.
Add 20 grams of salt to
container 2 and stir.
•
Add no salt to container
3.
3. Place the 3 containers in a
freezer.
•
4. Check the containers every
15 minutes. Record your
observations.
1.
The manipulated/independent
variable is the amount of salt added
to the water.
The responding/dependent
variable is how long it takes the
water to freeze.
The control is container 3, which has
no salt added. This allows you to
compare how long it takes regular
water and salt water to freeze.
Notice that the other factors, such as
the amount of water or starting
temperature are kept constant. This
ensures valid results and that only
one variable is tested.
Operational Definition
Before beginning the experiment, you must have a
clear operational definition. An operational
definition is a statement that describes how a
particular variable is to be measured or how a term
is to be defined.
For example, how will you determine if the water
is frozen? You might decide to insert a stick in
each container in the beginning of the
experiment . Your operational definition of
frozen could be the time at which the stick can
no longer move.
Materials
•
Before beginning the
experiment, make a
list of all the
materials you will
need to complete it.
Observation
You perform the experiment & see what
happens. You may need to take
measurements, pictures etc. depending on
the nature of the experiment.
Data
• The observations &
measurements you make
in an experiment are
called data. You gather
that data and organize it
into tables, charts or
graphs. Then think
through what the data
reveals. Does it support
your hypothesis?
Types of Data
• Quantitative Data:
Involves
measurements or
numbers. This data is
organized into graphs
(bar, line, etc.)
• Qualitative Data:
Involves descriptions
or words. This data is
organized into tables
or pictures.
Drawing a Conclusion
• A conclusion is a
statement that sums up
what you have learned
from an experiment. You
need to decide whether the
data you collected
supports your hypothesis
or not. You should repeat
an experiment several
times before you can draw
any conclusions from it.
Repeating the Work
• Before the conclusion of can be accepted by
the scientific community, other scientists
must repeat the experiment & check the
results.
• So when a scientist writes a report, it must
be detailed enough so that scientists around
the world can repeat the experiment for
themselves.
Find Flaws in this Experiment.
• Gerard wants to find out if egg yolk causes silver
to tarnish. He labels 2 silver spoons A & B. He
puts egg yolk on both spoons. Then he places
spoon A in a closed container and leaves spoon B
out in the open air. He checks the spoons over the
next few days.
• Flaws: Egg yolk, which is suppose to be the
variable, should not be put on both spoons.
Other factors, such as the exposure to air,
should be kept the same for both spoons.
Find Flaws in this Experiment.
• Daria wants to find out if fertilizer causes plants
to grow taller. She takes 2 plant shoots of the
same size & type and labels them A & B. She adds
fertilizer to plant A but not to plant B. Then she
places plant A in a sunny window and waters it
everyday. She places plant B on a bookshelf away
from the sun and waters it every other day.
• Flaws: The experiment has too many variables.
Daria has varied the amount of light and water
each plant receives. Except for fertilizer, all
other conditions should be kept the same.
Problem Solving
• Hypothesis: Turtle eggs develop into male
turtles in cold temperatures and into
female turtles in warm temperatures.
• Predict whether this hypothesis is fact or
fiction. Design a simple experiment to
show if the hypothesis is or is not correct.
Make sure your experiment has an
experimental setup and a control setup.
Practice Drawing a Conclusion
• Here is one way a biologist might design the
experiment. A great quantity of the same type of
turtle eggs are collected. Batches of 25 eggs are
out in containers at different temperatures.
After 60 days, the following data is recorded:
Temp.
26°C
28°C
30°C
32°C
Male
21
13
1
1
Female
2
11
19
20
Draw a bar graph
using the information
on this table. Write
a conclusion.