Transcript Notes on Experimental Design (Powerpoint)

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