Transcript Review of the Scientific Method

Review of the
Scientific Method
"The scientific method is nothing but
the normal working of the human
mind."
Thomas Huxley
What is the Scientific
Method?
 The scientific method is a planned,
logical, approach taken to solving a
problem
 It consists of asking a question,
developing a possible solution, testing
the possible solution, recording data, and
analyzing results
Steps of the Scientific
Method
 The basic scientific method consists of
five broad steps:
 Identifying the problem or question
 Developing a possible solution, or
hypothesis
 Designing and executing a test
 Collection and analysis of data
 The formulation of a conclusion
Identifying the Problem or
Question
 Identify a problem to be solved or a questioned
to be answered.
 To be scientifically valid, questions or problems
must be falsifiable.
 Usually scientists collect information about a
problem or question, before positing a possible
solution.
 The possible solution to a scientific problem or
question is known as a hypothesis
The Hypothesis
 A hypothesis is a possible solution to a scientific
problem or question.
 To be valid a hypothesis must be testable
 Ex. Which of the following are valid hypotheses?
The sky is blue due to the reflection of sunlight off the
Earth’s oceans.
The sky is blue due to the scattering of blue light by
oxygen in the atmosphere.
The sky is blue because a higher being made it that
way.
Procedure: What is an Experiment?
 An experiment is a test designed to prove or
disprove a hypothesis
 Experimental Design involves:
 Establishing controlled and uncontrolled
variables
 Establishing the independent and dependent
variables.
 Experiments generate data which scientists
record in tables, etc.
Collecting and Analyzing Data
• Data collection occurs as an experiment
proceeds.
• Usually data is numerical in form
• However, during an experiment
observations may be made that can
include temperature changes, the
formation of gas bubbles, changes in
color, etc.
Analysis of Data
 Numerical Data is usually analyzed by
determining the mean, median, and
mode.
 Numerical data is often graphed as a
means of visually determining
relationships between variables.
Conclusions
 After the data is analyzed a
determination must be made as to
whether the data supports or refutes the
hypothesis.
 If the data supports the hypothesis…
 If the data refutes the hypothesis…
 If the data is indeterminate…
An Example of
Experimental Design
Francesco Redi
Tests the Theory of
Spontaneous
Generation
Background –
Spontaneous Generation
 Until the seventeenth century experimentation
was treated as an art rather than science.
 Many strange, and now discredited, ideas
about how living organisms are propagated
flourished.
 The theory of spontaneous generation was a
very popular, ancient theory used to explain the
seeming production of many animals from nonliving materials.
Example One
 Observation: Every year in the spring, the Nile
River flooded areas of Egypt along the river,
leaving behind nutrient-rich mud that enabled
the people to grow that year’s crop of food.
However, along with the muddy soil, large
numbers of frogs appeared that weren’t around
in drier times.
 Conclusion: It was perfectly obvious to
ancient peoples that the muddy soil gave rise
to the frogs.
Example Two:
 Observation: In many parts of Europe,
medieval farmers stored grain in barns
with thatched roofs. As a roof aged, it
was not uncommon for it to start leaking.
This could lead to spoiled or moldy grain,
and of course there were lots of mice
around.
 Conclusion: It was obvious to them that
the mice came from the moldy grain.
Example Three
 Observation: Since there were no refrigerators, the
mandatory, daily trip to the butcher shop, especially in
summer, meant battling the flies around the carcasses.
Typically, carcasses were “hung by their heels,” and
customers selected which chunk the butcher would
carve off for them. Many times they would have to
remove maggots from the putrefying meat.
 Conclusion: Obviously, the rotting meat that had been
hanging in the sun all day was the source of the
maggots and flies
Redi’s Experiment
 Francesco Redi (1626-1697), an Italian
scientist, thought that the Theory of
spontaneous Generation was incorrect.
 In 1668 he designed what is thought to be the
first experiment explicitly designed via the
scientific method.
 The experiment tested the idea that maggots,
and therefore flies, are generated
spontaneously from rotting meat.
Redi’s Problem and Hypothesis
 Observation: There are flies around meat
carcasses at the butcher shop.
 Question: Where do the flies come from?
Does rotting meat turn into, or generate, the
flies?
 Hypothesis: Rotten meat does not turn into
flies. Only flies can make more flies.
 Prediction: If meat cannot turn into flies,
rotting meat in a sealed (fly-proof) container
should not produce flies or maggots.
Redi’s Test and Observations
No Cover
Cheesecloth Cover
Impervious Cover
Data: Presence or absence of flies and maggots observed in each jar was
recorded. In the control group of jars, flies were seen entering the jars.
Later, maggots, then more flies were seen on the meat. In the gauzecovered jars, no flies were seen in the jars, but were observed around and
on the gauze, and later a few maggots were seen on the meat. In the
sealed jars, no maggots or flies were ever seen on the meat.
Redi’s Conclusions
 Only flies can make more flies.
 In the uncovered jars, flies entered and laid eggs on
the meat. Maggots hatched from these eggs and grew
into more adult flies.
 Adult flies laid eggs on the gauze on the gauzecovered jars. Maggots appeared on the gauze.
 In the sealed jars, no flies, maggots, nor eggs could
enter, thus none were seen in those jars.
 Maggots arose only where flies were able to lay eggs.
This experiment disproved the idea of spontaneous
generation for larger organisms.
Controlled Versus
Uncontrolled Variables
 A controlled variable is any factor in an
experiment that is kept the same in all trials of
the experiment.
 Controlled variables are more commonly
known as Constants.
 Uncontrolled variables are those factors in an
experiment that are allowed, or chosen, to
change during the experiment.
 There are two types of uncontrolled variables:
Independent and Dependent
Independent versus
Dependent Variables
 The independent variable (aka: manipulated
variable) is the factor in an experiment that is
chosen, or manipulated by the experimenter.
 What was the independent variable in Redi’s
experiment?
 The dependent variable (aka: responding or
measured variable) in an experiment is the
factor that changes or responds to changes in
the independent variable.
 What was the dependent variable in Redi’s
experiment?
Control Group versus Experimental Group
 The control group in an experiment is the set of tests
in which nothing was manipulated by the experimenter.
 The control group is the standard by which all changes
in the manipulated tests are measured.
 What was the control group in Redi’s experiment?
 The experimental group in an experiment is the set of
tests in which the experimenter manipulates the
independent variable.
 What was the experimental group in Redi’s
Experiment?
Identifying Controls
and Variables
 Smithers thinks that a special juice will increase the
productivity of workers.
 He creates two groups of 50 workers each and
assigns each group a task (in this case they’re
supposed to staple a set of papers).
 Group A is given the special juice to drink while they
work. Group B is not given anything.
 After one hour Smithers counts how many stacks of
papers each group has made. Group A made 1,587
stacks, Group B made 2,113 stacks.
Identifying Controls
and Variables
What was Smithers’ ……
 Control Group?
 Independent Variable?
 Dependent Variable?
 What should Smithers’ conclusion be?
 How could Smithers’ improve his experiment?
Assignment:
 Work in pairs to complete “The Simpsons
Identifying Controls and Variables”
worksheet.
 If you do not finish the assignment in
class complete it as home work.
Yesterday’s
Classwork/Homework
 Identifying Experimental Variables and
Controls