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

Understanding Results in Science

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.)