Theory vs. Law, the remix

True or false?

• The difference between laws and theories is that laws are more true, they have more proof to back them up.– False!

• If a theory is tested enough, it will eventually become a law.– False!

Theory vs. Law, the truth!

• Both scientific laws and scientific theories are produced from the scientific method through the formation and testing of hypotheses, and can predict the behavior of the natural world. Both are typically well-supported by observations and/or experimental evidence. However, scientific laws are descriptive accounts of how nature will behave under certain conditions. Scientific theories are broader in scope, and give overarching explanations of how nature works and why it exhibits certain characteristics. Theories are supported by evidence from many different sources, and may contain one or several laws.

Theory vs. Law, the truth!

• A common misconception is that scientific theories are rudimentary ideas that will eventually graduate into scientific laws when enough data and evidence has been accumulated. A theory does not change into a scientific law with the accumulation of new or better evidence. A theory will always remain a theory; a law will always remain a law. A theory is valid as long as there is no evidence to dispute it. Therefore, theories can be disproven.

Some Examples

• Theory of Heliocentricity (The sun is at the center of the solar system)

• Cell Theory (Living things are made of cells)• Plate Tectonic Theory (Earth’s crust is made up of large

moving chunks)

• Law of conservation of energy• Euler’s first law of linear momentum

Assignment:

• For the next ten minutes, write a paragraph summarizing the difference between a law and a theory.

• Start by stating your thesis – explain the relationship.• Try to keep it simple and use the most succinct

argument possible.

Objectives:1. Students will be able to identify and

construct the different parts of an experiment.

2. Students will know the terminology related to experimental design:Variable, independent variable, dependent variable, levels of the independent variable, control, repeated trials, Prediction (hypothesis),

3. Students will understand how to use an experimental design diagram and the four questions strategy

What is an Experimentand

What is not an Experiment• An experiment can be a test of the effect

of different actions carried out by the experimenter

• A test comparing differing conditions as some action is carried out.

An Experiment is not

• An exercise to measure the density of a piece of metal.

• A survey of different types of plants or animals along a beach.

• An experiment starts and finishes with the factors that change during the experiment

• These factors are called variables.

Independent and Dependent Variable

• The independent variable is the one the experimenter purposely changes.

• The dependent variable changes in response to the purposeful change.

What is the independent and what is the dependent

Variable

There are many other factors that could be changed by the experimenter, and have an effect on the outcome of the experiment.

• Factors that could be changed but which are deliberately held constant are referred to as Constants.

Levels of the Independent Variable

• Often the independent variable that is manipulated by the experimenter will have several different values.

• Allows the testing of only one variable at a time.

• One of the levels of the independent variable will serve as a reference point or “normal” value of which the other levels will be compared to.

• This is the Control!

• Every experiment should be carried out several times and then the results of the individual trials averaged together.

• Makes for a more reliable test, and decreases the possibility of obtaining a misleading result.

So, How many trials should you do?

• The general rule is that students should repeat the experiment as many times as it is convenient and practical to do so.

Formally known as the Hypothesis

• Written in the form of a “if-then” statement.

• Linking the independent variable to the dependent variable.

• Based on the student’s past experiences as well as information they have been able to gather while carrying out background research.

General Layout for an Experimental Design Diagram

• TITLE• The Effect of _________________________ (Independent Variable) on _________________________________ (Dependent Variables)

• HYPOTHESIS• If ________________(planned change in independent variable), then _____________(predicted change in dependent variables).

• INDEPENDENT VARIABLE ___________________________________ • LEVELS OF INDEPENDENT VARIABLE AND NUMBERS OF REPEATED TRIALS

• DEPENDENT VARIABLE AND HOW MEASURED• ___________________________________________________________________• CONSTANTS• 1.• 2.• 3.• 4.

level 1 (control) Level 2 Level 3 level 3 Level 4

Number of Trials

Number of Trials

Number of Trials

Number of Trials

Number of Trials

Four-question Strategy

1. What materials are readily available for conducting experiments on general topic of interest?

2. What action is observed when studying general topic of interest?

3. What are all the ways that I can change the set of materials that would change the action?

4. In what ways can I measure of describe the response to the change?