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Big Idea 3: The Role of Theories, Laws,
Hypotheses, and Models
The terms that describe examples of scientific knowledge, for example; theory, law, hypothesis, and model have very specific
meanings and functions within science.
SC.8.N.3.1 Select models useful in relating the results
of their own investigations. SC.8.N.3.2 Explain why theories may be modified but
are rarely discarded.
Benchmark Number & Descriptor
Models are developed in an effort to explain how things in nature work.
Types of models◦ Physical constructions◦ Detailed pictures◦ Equations and graphs
MODELS
A scaled version of what is being investigated◦ Real versions may be
too small, big or dangerous to handle.
◦ Must contain the correct amount of details Too little – model is
worthless Too much – model is
complicated
PHYSICAL CONSTRUCTIONS
Diagram that visually represents information helps:◦ to organize facts◦ to show
relationships◦ to analyze and
interpret findings
DETAILED PICTURES
A Food Web in Terrestrial and Aquatic Ecosystem
Equations◦ Mathematical
expression of scientific theories
Graphs◦ Visual
representation of data
◦ Show relationships between variables
E = MC2
F = MA S = distance/time
X axis = independent variable
Y axis = dependent variable
EQUATIONS and GRAPHS
Knowledge Check 1. Why do scientists use models?
2. List three types of models scientist use? 3. When using graphs, where are the
variables located?
Knowledge Check 1. Why do scientists use models?
◦ To help explain and represent their findings 2. List three types of models scientist use?
◦ Physical constructions◦ Detailed pictures◦ Equations and graphs
3. When using graphs, where are the variables located? ◦ Independent = X-axis◦ Dependent = Y-axis
After experiments have been completed and observations and conclusions have been made, a theory may be created.◦ Set of ideas that link together many observations
of the same experiment.
A theory is created…
Start with an observation that evokes a question: Broth spoils when I leave it out for a couple of days. Why?
Using logic and previous knowledge, state a possible answer, called a hypothesis: Tiny organisms floating in the air must fall into the broth and start reproducing.
Perform an experiment or test: After boiling some broth, I divide it into two containers, one covered and one not covered. I place them on the table for two days and see if one spoils. Only the uncovered broth spoiled.
Then publish your findings in a peer-reviewed journal. Publication: "Only broth that is exposed to the air after two days tended to spoil. The covered specimen did not."
Other scientists read about your experiment and try to duplicate it. Verification: Every scientist who tries your experiment comes up with the same results. So they try other methods to make sure your experiment was measuring what it was supposed to. Again, they get the same results every time.
In time, and if experiments continue to support your hypothesis, it becomes a theory: Microorganisms from the air cause broth to spoil.
Development of a Simple Theory by the Scientific Method:
http://wilstar.com/theories.htm
Is That Theory Your Final Answer…
ACCEPTED THEORIES DISPROVEN THEORIES
Theory has been confirmed over many independent experiments.
Examples:◦ Theory of Gravity◦ Theory of Relativity◦ Quantum Theory
An experiment could show that a hypothesis is incorrect.
A scientist is expected to propose a better theory to fill in that gap in our knowledge.
Examples: ◦ The Earth is the center of the
universe.◦ Flat Earth Theory◦ The classical elemental theory
Knowledge Check 1. What is a theory?
2. How might a theory be disproven? 3. List and explain a theory which still
stands and one that has been disproven?
Knowledge Check 1. What is a theory?
◦ Set of ideas that link together many observations of the same experiment
2. How might a theory be disproven?◦ New information or technology is applied to an existing
theory, and the published results are not verified. 3. List and explain a theory which still stands and
one that has been disproven? ◦ Theory = Theory of gravity (Every object in the universe
attracts every other object in the universe)◦ Disproven Theory = Geocentric theory (Earth is the center
of the solar system.)