## Sunday, September 11, 2011

### Apologia General Science, Module 3, How to Analyze and Interpret Experiments

What we did at Sahm-I-Am

Students:
• Quizlet M3

Parents:
Thinking Objectively
See this and more at Debbie's Educator's Resources.  (Thanks, Debbie!)

(1) p. 58-63a, Experiments and Variables
Independent variables vs. dependent variables.
An independent variable is what you decide.
A dependent variable depends on what you decided.
In Exp. 1.1, A Floating Egg, it was decided how much salt should be put into the water.
That was the independent variable.
What happened to the egg was the dependent variable.
The more the independent variable (amount of salt) changed, the more the dependent variable (how much the egg floated) changed.

It is important to note that some variables do not affect the experiment enough to really count.
However, you should always reduce as many variables as possible that are not necessary for the experiment.
Another thing to keep in mind is to only change ONE variable at a time.
(Remember my daughter's computer screen.)
In the egg experiment, you changed the amount of salt, but you did not increase or decrease the amount of water, or the size of the egg, or the glass.
Some of these variables would obviously change the experiment more than others, such as an increase in the amount of water could reduce the salt-to-water ratio.

Reducing the number of variables - you should only have one experimental variable.  Everything else should be the same.

Part 1

Part 2

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(2) p. 63b-69, Using a Series of Experiments
In this section, we did a series of experiments to show that soap decreases the surface tension of water.
We also learned about the importance of having a control for your experiment.  A control is the variable or part of the experiment to which all others can be compared.  Simply put, a control is the variable in which nothing is changed.  It was the part that had no experimental treatment.

Surface Tension - 36 drops of water on a penny

Surface Tension

Another thing that could be done instead of tipping the screen-covered jar, is to spray some soapy water onto the screen.  Soap molecules interfere with water's surface tension.

What does soap do?

Review:  Controlling variables - making sure everything is the same except for the variable being tested.

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(3) p. 70-73a, Recognizing Experimental Variables When They are not Obvious

The Scientific Method (with a funny video clip), and Recognizing Variables
control is the variable or part of the experiment to which all others can be compared.  It is the part that receives no experimental treatment.
placebo is a fake pill that contains no medication.
►You can see the funny part again here.  =)

Control groups and Blind Studies

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(4) p. 73-76, Interpreting the Results of Experiments
Which type of graph to use?

Remember:
Line and bar graphs are done in the 1st quadrant so that you only see ¼ of  a whole graph.
(See image.)
The Independent Variable (what you decide) goes on the bottom on the x axis.  It will increase in even increments, and you mark those across the bottom.
The Dependent Variable (what changes) goes on the left on the y axis, and again, should be marked in increments.  The results will vary, going up or down.

In this line graph, the independent variable is indeed on the bottom with the dependent variable on the left.
You can see that the independent variable, time, is on the bottom.  The increment of time was decided by the person doing the experiment.

See the first bar graph here.
Patients were then given either a real medication or a placebo.
The dependent variable, the results, are written in increments on the left of the graph so you can see these results at a glance by how far the bar extends upwards or how far up or down the line is graphed.