Designing an Experiment : Lesson 7 Designing an Experiment
Objectives : Objectives Use space/time relationships, define concepts operationally, raise questions, and form testable hypothesis.
Design a controlled experiment by specifying how the independent variables will be manipulated, how the dependant variable will be measured, and which variables will be held constant.
State Standards : State Standards Pennsylvania State Science Standards
3.2. – Inquiry and Design
3.2.7.B – Apply process knowledge to make and interpret observations.
Controlled Experiments : Controlled Experiments Controlled Experiments – only one variable or condition changes at a time.
Watch the following video of a controlled experiment.
controlled experiment
Helps scientists know how each variable affects the experiment.
Practice Problem #1 : Practice Problem #1 What is the best way to find out which part of a bicycle is squeaking?
A. oil all parts of the bicycle
B. oil one part of the bicycle at a time
C. ride the bicycle until the squeaking stops
D. take the bicycle apart and put it back together. B. Is correct, because you are changing one variable at a time
Controlled Experiments : Controlled Experiments Control Group
Experimental Groups
What type of fertilizer is best for tomato plants?
Controlled Experiments : Controlled Experiments Independent Variable
Dependant Variable
Evaluating the Dependant Variable : Evaluating the Dependant Variable When designing an experiment, you need to be very precise about what you want to learn.
To evaluate the dependant variable:
What will you measure?
How will you describe it?
The hypotheses needs to be testable answer or explanation.
Practice Problem #2 : Practice Problem #2 Which hypothesis would be most appropriate for the fertilizer experiment with tomato plants?
Two out of three farmers will prefer fertilizer A
Fertilizer A will make the plants grow better than fertilizer B will.
Fertilizer B will cause the tomato plants to grow taller than fertilizer A will.
Plants given no fertilizer will do worse than plants that are given fertilizer
Designing a Controlled Experiment : Designing a Controlled Experiment Scientific question
Good hypotheses
How many experimental groups
How will the independent variable be manipulated
What kind of observations will be made
How is the dependant variable going to be measured What kinds of tools will be used
What units would be used for the data
Practice Problem #3 : Practice Problem #3 Consider Mario’s experiment with water vapor and air temperature.
Identify the independent variable and the dependant variable in the experiment.
Describe how Mario planned out the experiment so that he could be sure that the amount of water in the air was the only main factor affecting the air pressure.
Key Vocabulary : Key Vocabulary Controlled experiment
Control group
Experimental group
Independent variable
Dependant variable