Overview of Scientific Method
Ask a Question
Research
(if necessary)
Form a Hypothesis
List Materials Needed
Decide Steps in
Procedure
Perform Experiment
Analyze Results
Draw a Conclusion
Science Skills
Observing & Inferring
Observing-using one or more of your senses to gather information about
the world.
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-the senses include: sight, hearing, smell, taste, and touch
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-observations should be accurate and objective
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-to be accurate means you give an exact report of what your
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senses tell you
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-qualitative observations: no numbers, include information
such as colors, smells, tastes, textures, or sounds.
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-quantitative observations: include numbers, counting
objects. Often made using tools to take measurements (ruler,
etc.).
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inference- explaining or interpreting an observation or statement.
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-example: walking into your house, smell fish cooking and
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think, “We’re having fish for dinner.”
-to be objective means opinions, or specific points of view
are not part of your observation.
-observations can be either qualitative (quality) or quantitative
(quantity)
Name: ____________________________________ Date: _______
Understanding Hypotheses
You already know that the scientific method provides an organized way
to investigate a question. Once you have a question that you want to
investigate and have done some research on it, the first step in the scientific
method is to express that question in terms of a hypothesis. A hypothesis is
an idea about how what you are investigating works. A hypothesis is often
stated as a condition (if) and a result (then).
Example: If I add fertilizer to my plants, I will get more flowers.
A hypothesis is a prediction about what you think will happen if you try
the condition. A good hypothesis must be testable. A hypothesis must be
written carefully so that you can measure both the condition and the result.
Is the example hypothesis testable?
A hypothesis is testable if you can create a controlled experiment that
will give you more information. This hypothesis is testable because you can
experiment with two groups of plants of the same species. One group would
get a measured amount of fertilizer, like one tablespoon, on a regular
schedule and the other group of plants wouldn’t get any fertilizer. Then at
the end of the experiment you can measure, or count, the number of flowers
on the plants in each group.
An untestable hypothesis: If I eat more protein, my muscles will be stronger.
There are two reasons why this is not a well-defined hypothesis. If you
tried to design an experiment from this hypothesis, there is no control group
to compare to. Second, “get stronger” can’t be measured. Think of some
ways that you could measure “get stronger.” Did you think of lifting heavier
weights, running further, or doing more pull-ups? These are three different
ways of measuring strength in a human.
Exercise: Write a testable hypothesis for the following statement.
Statement: Proper tire pressure improves gas mileage.
Hypothesis: If the tire pressure for a car is set at the manufacturer’s
recommended amount, the gas mileage of the car will increase.
How would you test this hypothesis?
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Name: ____________________________________ Date: _______
Understanding Dependent and Independent Variables
As part of the scientific process, researchers, scientists and even
ordinary people conduct experiments every day to find out more about the
world we live in. An experiments needs to be carefully designed to make sure
it accurately measures what it is supposed to so that the results are correct
and so that the experiment can be repeated by someone else.
Basic experiments are based upon a hypothesis that tries to predict
the outcome of the experiment. Many experiments do not show that their
hypothesis is true. These experiments are still valuable because they help to
guide further research into an area that scientists are interested in.
Experiments test the influence of one thing over another. A proper
experiment compares two or more things but changes only one variable or
factor in the experiment. One example that is often used is an experiment
that tests the influence of fertilizer on the growth of plants. The hypothesis
states that plants that get fertilizer grow taller than plants that get no
fertilizer.
For any particular plant in the experiment, the amount of fertilizer it
will get during the experiment is determined in advance by the experimenter.
Some plants will get no fertilizer while others will get a measured amount. In
this example, the independent variable is the amount of fertilizer.
The other term used in experiments is dependent variable. The
dependent variable is what is measured in the experiment. In this example,
the dependent variable is how tall the plants are. The dependent variable
(how tall the plants are) depends on the independent variable (the amount of
fertilizer).
Example:
Stress increases the heart rate of a person.
Dependent variable (what is measured in the experiment):
heart rate
Independent variable (what is controlled in the experiment):
the amount of stress
Exercise:
Lifting weights increases the breathing rate of a person.
Dependent variable: _______________________
Independent variable: ______________________
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Name: ____________________________________ Date: _______
Understanding Control and Experimental Groups
The way to show that a hypothesis is true or false is to design and
complete an experiment. Scientists must be careful in how they design an
experiment to make sure that it tests exactly what the hypothesis states. A
proper experiment compares two or more things but changes only one
variable or factor in the experiment.
In order to make sure that only one factor is being changed in an
experiment, the test is divided into two groups. One group, called the control
group, is exposed to the all the circumstances of the experiment but doesn’t
get whatever factor is being tested in the experiment. At the same time, the
experimental group gets all the circumstances of the experiment plus the one
variable being tested by the experiment.
Let’s look at an experiment designed to determine if adding fertilizer to
plants will result in more flowers. If a scientist was testing the flower and
fertilizer hypothesis, she would select one species of flower to test with, let’s
say petunias, and buy a dozen plants. Six of the plants would be the control
group and six the experimental group. All the plants would be kept in the
same greenhouse and given the same amount of light and water. The
experimental group of six petunia plants would get a measured amount of
fertilizer on a regular schedule while the control group of the other six
petunias would not get any fertilizer.
The purpose of the control group in an experiment is to provide a fair
base for comparison when it’s time to analyze results. For example, what
would happen if the scientist compared her fertilized greenhouse plants to six
petunia plants growing in the yard? The plants outside were watered by
natural rainwater, were growing in different soil and had different
temperatures than the plants in the greenhouse. If there was a difference in
the number of flowers, how would she know if it was due to the fertilizer and
one of the other variables?
Having a control group is one of the most important parts of
conducting an accurate experiment.
Example:
Hypothesis: Puppies that are given vitamins gain more weight.
Control group: puppies that aren’t given vitamins
Experimental group: puppies that are given vitamins
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Name: ____________________________________ Date: _______
Writing Experiment Conclusions
The purpose of conducting an experiment is to be a detective and
decipher the answer to a question that interests you in an organized way
using the scientific method. Writing your conclusion is an important part of
the investigation. You want to share with everyone else what you found out
in your sleuthing.
Since you’ve been following the scientific method throughout your
investigation, you want to write an organized conclusion that summarizes
your experimental findings in a clear and complete way. You write the
conclusion after you finish the experiment and graph the data.
The conclusion gives a snapshot of what you accomplished so it
contains summary information about the experiment as well as the
conclusions. Here are the important points that a well-written conclusion
includes:
1. Restatement of the hypothesis. This sentence reminds your audience
what you set out to accomplish.
2. Short summary of the experiment. The summary includes just one or
two sentences that explain how the experiment was conducted.
3. What the data shows. State what the data showed in one or two
sentences.
4. Your conclusion. Clearly state how the data supports or doesn’t
support the hypothesis. Be accurate; an experiment that does not
support its hypothesis is just as valuable as one that does.
5. Changes to the experiment. Write a sentence that indicates how the
experiment could be improved.
6. What next? Give an idea of what question you’d like to explore next
on this topic. This idea is related to the experiment you just did.
Example conclusion:
My hypothesis was that coleus plants that were given fertilizer would grow
taller than plants without fertilizer. I used two sets of coleus plants kept under
the same conditions except for the amount of fertilizer. The coleus plants given
one teaspoon of 10-10-10 fertilizer grew on average 2 ½ inches taller than
plants without fertilizer. If I were to conduct this experiment again I would add
another group of plants and give them 2 teaspoons of fertilizer to see if these
plants would grow even taller. Because of the results of this experiment, I
wonder if adding fertilizer would cause plants to produce more flowers as well as
grow taller.
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