Experimental Design using Scientific Method:

Experimental Design using Scientific Method:
Experimental Design using
Scientific Method:
When scientists begin an
experiment they use the
steps of the Scientific
Method. You will be asked
to understand many of
these steps on the STAAR
Test next year.
Scientific Method
– a logical step by step
way of solving problems
The Problem (in the form of a
question) that the scientists will try
to answer, must be logical and based
on data or observations.
Problem
- what you want to
learn or understand
A prediction called a Hypothesis is
next. It must be a testable
statement that you could gather
data to prove. (You can’t measure
which is the “prettiest”,
“strongest”, or “best”.)
Hypothesis
– an educated guess to explain what
you observe or what might happen
Testable –
can be proven true or false with data
You must control an experiment. You can test
only one variable at a time. (How does the
amount of water effect plant growth? Keep
the light, containers, soil and plants the
same.)
Controls: Light, type of plant,
amount of soil, pot, temperature.
Control
–what you do not
change in an
experiment
Variable
– what changes in an
experiment
500ml
400ml
300ml
A Control Group is the set-up that
isn’t changed. (One plant gets the
normal amount of water!). Which
group above is the control group?
The independent variable is the thing you
change (amount of water). The dependent
variable is the result of the change you made
(height of plant in cm.).
Independent
variable: Amount of
water given in ml.
Dependent variable:
Plant growth in cm.
Independent variable
– what I change in an
experiment on purpose
Dependent variable
– what changes because of
changing the independent
variable
DRY MIX = Dependent
Responding Variable on
Y-axis
Manipulated
Independent Variable on
X-axis
Growth in mm
When reporting the
results, the Independent
Variable is graphed on
the X-axis. The
Dependent variable is on
the Y-axis.
Amount of Water
The Conclusion must be supported by the data &
results you gather. To be valid, each experiment
needs a large sample size(grow 2000 plants in
each experiment) and must be repeated many
times in order to prove the Hypothesis (grow
2000 plants 100 times). If you are collecting
samples, in an experiment, do it randomly.
Don’t take them all from one place.
Yes!
No!
Conclusion
– what you have learned
(hypo true?)
valid
- true, trusted, reliable
Check for understanding
Check for understanding by answering
the following questions.
Remember that you are using the scientific
method (scientific reasoning and
investigating skills).
Which of these is a hypothesis that can be
tested through experimentation?
F Bacterial growth increases as temperature
increases.
G A fish’s ability to taste food is affected by
The pH of aquarium water.
H Tadpoles’ fear of large insects increases as
the tadpoles age.
J The number of times a dog wags its tail
indicates how happy the dog is.
The correct answer is F. Bacterial
growth can be measured. Dog
happiness, fish taste, and tadpole
fear cannot be measured
scientifically.
The table shows times required
for water to evaporate from
identical containers. Which of
these is the best question to ask
before developing a reasonable
hypothesis to explain the data?
A Does a lower temperature slow
the rate of evaporation?
B What is the boiling point of
the water after both samples are
heated?
C Why does water exist as a
solid at -15°C and as a liquid at
25°C?
D How does the rate of
evaporation change when a
different container is used?
The correct answer is A. The
table shows data taken to
investigate temperature and
the evaporation of water.
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