1. 10-2-17 Parts of an Experiment

2. Do Now: Answer the following question in your science notebook
What do you think are some essential parts of a good experiment?
Variables
Independent
Dependent
Constants
Groups
Experimental
Control
Repeated Trials

3. Repetition and Replication Quiz ReviewB. C
Replication
Repetition

4. Important Dates
Last Day to Complete any Missing Quizzes is Thursday, 10/5
First Day of Science Club is NOW Thursday, 10/5
The quarter ends Friday, 10/6

5. Parts of an Experiment
Standard SC.7.N.1.4 – Identify test variables (independent variables) and outcome variables (dependent variables) in an experiment.
Lesson Objective: I can identify the parts of an experiment

6. Key Vocabulary Independent variable Dependent variable Constant
Control group
Experimental group
Repeated trials

7. Parts of an Experiment Variables (Independent and Dependent Variable)
Constants
Groups (Experimental and Control)
Repeated Trials

8. Variables (Independent and Dependent)
An experimental investigation is an organized process used to test an idea. In a good experimental investigation, one must eliminate error to ensure that the results are due to the factor being tested.
Example: Kaitlin is trying to determine how pH affects the germination rate (the time it takes for the seeds to sprout).

9. Kaitlin filled three different size cups (3, 10, and 16 ounces) with soil.

10. She placed the following number of beans into each cup:
3 ounce cup: 1 bean
10 ounce cup: 8 beans
16 ounce cup: 6 beans

11. She covered the beans with soil and added water to the cups
She covered the beans with soil and added water to the cups. The water had been treated with chemicals to alter the pH. She added the following amounts of the different pH solutions to the cups:
3 ounce cup: 3 ml of water solution with a pH of 3
10 ounce cup: 10 ml of water solution with a pH of 7
16 ounce cup: 16 ml of water solution with a pH of 9

12. She placed the cups on the window sill for 5 days and got the following results:
She concluded that the pH did not affect the germination rate, since the cups with a pH 7 and pH 9 each had one bean germinate.
Was Kaitlin’s conclusion correct? Can we make any inferences based on her experiment?

13. Can we tell what caused the results of Kaitlin’s experiment?
An experimental investigation is a “fair test” designed to gather evidence to support or refute a causal relationship.
Can we tell what caused the results of Kaitlin’s experiment?
No. Kaitlin did too many things differently in the experiment.
Each cup was a different size
There was a different amount of soil in each cup
She planted varying amounts of beans in the cups
Each cup received a different amount of water

14. Variables Variable: something that changes
Independent variable: a characteristic of an experiment that determines the value of the other (dependent) variable(s).
Dependent variable: a characteristic of an experiment that is a result of the effect or influence of an independent variable.

15. Independent Variable Changed on purpose by the experimenter
Also called the test or manipulated variable
Considered the cause, the stimulus, or reason.

16. Dependent variable Acts in response to the independent variable
Also called the outcome or responding variable
Measured or observed
Is considered the effects or the results of the experiment

17. Think-Pair-Share: Think alone about the following questions for 30 sec
Think-Pair-Share: Think alone about the following questions for 30 sec. Then, pair with your table partner to answer the questions. Share with the class
Can you tell by looking at her original purpose what the independent variable should have been? pH
The independent variable should always have different levels or degrees. In Kaitlin’s experiment, what were the different levels of pH she tested?
The different levels of pH were 3, 7, and 9.
What was Kaitlin’s dependent variable in this experiment? What results was she looking for?
The germination rate (time it takes for the seeds to sprout).

18. Constants
Kaitlin had too many independent variables in her experiment. What should she have done with all the other variables, such as amount of water, size of cup, number of beans, and amount of soil?
She should have made them constants. In other words, she should have kept all of these the same throughout the experiment.
Constants: all factors in the experiment that are not allowed to change throughout the entire investigation

19. Kaitlin’s Experimental Design
“Fair Test” Experimental Design
3 different size cups (3 oz, 10 oz, and 16 oz)
Same size cup (10 oz)
Different amounts of soil. (She filled the different size cups to the top. Since they were different sizes, they each held different amounts.)
Same amount of soil (225 mL of soil)
Number of beans (1 bean, 8 beans, 6 beans)
Same number of beans (6 beans)
Amount of water (3 mL, 10 mL, 16 mL)
Same amount of water (16 mL)

20. Student Work:
A chart like the one below is a helpful tool when trying to organize the parts of an experimental investigation. Complete the chart below to help Kaitlin redesign her experiment.

21. Correct Answers

22. HW for Tonight:
Experimental Design chart

23. Groups (Experimental and Control)
Independent variables should have different levels or degrees. In Kaitlin’s experiment, the different levels of the independent variable were pH of 3, pH of 7, and pH of 9.
Usually, one of the levels of the independent variable is the reference point or “normal” value of the variable. The other levels will be compared with this one in order to draw conclusions from the experiment. This is called the control group.
Control group: a standard of comparison for checking or verifying the results of an experiment where all variables must be held constant
In Kaitlin’s experiment, the group of beans that was watered with the liquid that had a pH value of 7 would be the control group.

24. Groups (Experimental and Control) cont.
The other levels of the independent variable are referred to as the experimental group(s).
Experimental group: the group(s) being tested with the independent variable.
Each experimental group should only have one factor different from each other, everything else must remain constant.

25. Think-Pair-Share:
What were the experimental groups in Kaitlin’s experiment?
Beans with the solution of pH of 3 added to them and beans with the solution of pH of 9 added to them.

26. Repeated Trials
Repeated trials: a way to validate data by performing an investigation multiple times.
Each level of the independent variable should be repeated.
In general, the more times you repeat the experiment, the more valid your results are. The possibility of obtaining misleading or inaccurate results due to experimental errors will be less.
Every experiment should be carried out several times and then the results of the individual trials averaged together.
As a general rule, the experiment should be repeated at least 3 times.
In Kaitlin’s experiment, she did not have repeated trials. She planted more than one bean in each cup but she should have planted the beans in at least 9 cups and watered three cups with each level of pH solution.