The Scientific Method*
 Making observations
 Asking questions
 Developing a hypothesis
 Designing an experiment
 Collecting data
 Making inferences
 Results (peer review)
Experimental Design
 *Experiment: def. – an investigation consisting of
procedures that tests a hypothesis by collecting
data under controlled conditions.
 Investigation
 Procedures
 Controlled conditions
Control vs. Experimental Group
 *Control: def – the standard in which all
conditions in the experiment are kept the
SAME
 *Experimental (test) group: def – all
conditions are kept the same except for the
condition in question being tested
 Why do we need both groups?
Flaming Dollar Revisited
 Question: What is the effect of the amount
of isopropyl alcohol on the dollar bill’s
burning intensity?
 What is the Control Group?
 What is the Experimental Group?
Flaming Dollar Control Group
 (Control: def – the standard in which all
conditions in the experiment are kept the
SAME)
 Control group – soak the dollar bill in ONLY
WATER. (NO ALCOHOL IN SOLUTION)
Flaming Dollar Experimental Group
 (Experimental group: def – all conditions
are kept the same except for the condition in
question being tested)
 Experimental group – soak the dollar bill in
varying concentrations of isopropyl alcohol.
(testing the effect of amount of alcohol)
Variables
 *Independent variable: def – the one
condition that is tested because it
affects the outcome of the experiment
 *Dependent variable: def – the
observable condition that “depends” on
changes made to the independent
variable
Flaming Dollar Revisited
 Question: What is the effect of the amount
of isopropyl alcohol on the dollar bill’s
burning intensity?
 What is the Independent Variable?
 What is the Dependent Variable?
Flaming Dollar Independent
Variable
 (Independent variable: def – the one
condition that is tested because it affects the
outcome of the experiment)
 Independent variable – the amount
(concentration) of alcohol used in solution
to soak the dollar bill
Flaming Dollar Dependent Variable
 (Dependent variable: def – the observable
condition that “depends” on changes made
to the independent variable)
 Dependent variable – the burning intensity
that depends on the different amounts of
alcohol used.
FINAL THOUGHT!
 *ONLY TEST ONE variable at a time!!!
 Example: Flaming Dollar
 Amount of alcohol used
 Different $ bill amounts used
MUST TEST SEPARATELY!!!