This is the second Investigation of the LabLearner CELL Exploring Electricity. In this Investigation, students explored the interaction of electric charges in more detail.

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A. Begin the analysis of the experiments by reviewing several of the concepts introduced thus far in Investigation Two.  The following questions can be used to initiate a discussion of these concepts.

1. Ask students: What were the two main questions asked during the Lab? What happens when materials or objects have electrical charges?  What happens when two materials or objects have the same electrical charge?

2.  Ask students: Can you describe what you did in your experiments to answer the questions? Students should suggest that to answer the first question, they rubbed a balloon with the wool and held both the balloon and wool over the skin of their forearm.  They also rubbed a balloon with the wool and held both the balloon and the wool over plates of pepper.  To answer the second question, they rubbed two balloons with wool, then moved the balloons toward each other.

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B. Continue to review the Lab experiments.  Students may wish to refer to their Student Data Record during the review.  Ask students the following questions about Trials 1 and 2 to prompt discussion.

1. Ask students: In Trial 1, what occurred when you held the balloon and wool over your forearm without rubbing them? Students should indicate that the hair on their forearm remained in place and the balloon did not stick to their arms.

2. Ask students: In Trial 2 you rubbed the balloon and wool together.  What did you observe when you held them over your forearm after they were rubbed? Students should indicate that the hair on their forearm stood up toward the balloon and wool.

3. Ask students: Did you feel or hear anything when you held the wool and balloon over your arm? Yes.  Student answers may vary.  They may find describing this sensation difficult but should indicate that they could feel a fuzzy, tingling sensation.  They may indicate that the sensation felt as if something is pulling up toward the balloon.  They may also have heard a faint crackling as they moved the balloon and wool over their arm.

4. Ask students: What term or terms would you use to describe the sensation? Student answers may vary.  Encourage students to describe the interaction between the hair and the wool or balloon as the attraction of the hair to the balloon or wool, as the result of static electricity.

5. Ask students to think about what they observed and felt when they held the wool and balloon over their forearms.  Was there a difference between what you felt and observed when you held the wool and the balloon over your arm? Yes.  The sensation and crackling were not as strong when the wool was used as when the balloon was used.  The attraction between the wool and hair was not as great as between the balloon and hair.

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C. Encourage students to continue their analysis by focusing on the results of Trial 3.

1. Divide students into 5 cooperative groups.

Point to the two questions presented on this slide.  

Explain that you would like students to think about what they have discussed thus far and to work with the other members of their group to answer the questions.

a. What occurred in Trial 3 when the balloon and wool were rubbed together and held over the pepper?  Was there a difference between the balloon and wool? Pepper was attracted to both the wool and balloon.  However, the pepper easily left the paper plate and stuck to the balloon, but only a small amount of pepper left the paper plate and stuck to the wool.  There was more attraction between the pepper and balloon than the pepper and wool.

b. What can you conclude about electrically charged and neutral objects from your experiments? Students should suggest that, since the hair and pepper moved toward the balloon and wool after the balloon and wool were rubbed together, then the objects that had electrical charges could attract objects that were neutral. 

2. After several minutes, encourage students to share their answers with the other groups.

3. Ask students: Did your experiments help to answer the question you were asked before the Lab, “What happens when materials or objects have electrical charges?” How? Students should indicate that their lab experiments helped to answer the question.  They created static electricity and objects with electrical charge by rubbing the wool and the balloon.  When the two objects with electrical charges were brought into close contact with neutral objects, the objects were attracted to each other.  The attraction of the hair and pepper to the positively charged wool and negatively charged balloon was a result of static electricity.  

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4. Ask students to locate Problem 7 of their Student Data Record.

a. Explain that they will use the Table to organize and record their results and conclusions from Trials 1-3.

b. Tell students to think about what they recently discussed and then to label each object as neutral, positively charged, or negatively charged.  Allow students time to complete the problem independently or in pairs to help them rehearse what they have learned.  After sufficient time, work through the problem with the students to check their understanding of the events in each trial.

5. Conclude this part of the analysis by asking students to apply their knowledge to the following question:

Ask students: Why do you think the wool did not attract as much hair or pepper as the balloon? Student answers may vary.  They should suggest that the wool and balloon are made of different types of materials and that the wool may not be a material that becomes as charged as the balloon.

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D. Remind students of the second question they investigated in the Lab:

What happens when two materials or objects have the same electric charge?

1. Ask students:  What did you do to determine the answer to the question? Students rubbed two balloons with wool, then moved the balloons toward each other.

2. Pose the following questions about Trials 4 and 5 to prompt discussion:

a. Ask students: In Trial 4, you did not rub the balloons.  Were the balloons charged or neutral?  The balloons were neutral.

b. Ask students: What did you observe when you moved the neutral balloon “A” toward neutral balloon “B,” the balloon hanging from the string?  Students should indicate that they did not observe attraction between  the balloons or a great deal of movement between the balloons.  Should students state that they observed balloon “B” move slightly or spin around, this indicates that one or both of the balloons picked up a small amount of electrical charge as it was handled.

c. Ask students: In Trial 5, you rubbed both balloons with wool.  Were the balloons neutral or charged?  Why?  Both balloons were negatively charged because as wool is rubbed against the balloons, it transfers some electrons to the balloons.

d. Ask students: What did you observe in Trial 5 when both balloons were negatively charged?  After rubbing both balloons and moving balloon “A” toward balloon “B,” it was observed that balloon “B” moved away from balloon “A.”

e. Ask students: What can you conclude about objects with the same charge?  Students should suggest that, since both balloons were negatively charged and they moved away from each other, then objects with the same electrical charge repel each other.

f. Ask students: Did your experiments help answer the question, “What happens when two materials or objects have the same charge?”  How?  Students should suggest that they created two objects with the same charge and observed that they moved away from each other.  This result suggests that when two materials or objects with the same charge are brought into close contact, the two objects repel each other.

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3. Tell students to locate Problem 7 of their Student Data Record.  

a. Explain that they will use the Table to organize and record their results and conclusions from Trials 4 and 5.

b. Tell students to think about what they recently discussed and then to label each object as neutral, positively charged, or negatively charged. 

Allow students time to complete the problem independently or in pairs to help them rehearse what they have learned.  After sufficient time if students are having difficulty, work through the problem with the students.

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E. Complete the analysis by reviewing and extending the concepts introduced during Investigations 1 and 2 posing the questions that follow.

1. Remind students that every object or material has a specific number of electrons and protons.

a. Explain that objects or materials have a neutral electrical charge unless they are rubbed or come in close contact with another object or material.  

b. Ask students:  Do you think there is a point at which rubbing objects such as the balloons and wool would no longer produce a transfer of electrons? Student answers will vary.  Yes.  Since an object or material only contains a specific number of electrons and protons, then only the number of electrons contained in that object or material could transfer.  There would be a point in which no more electrons would transfer.

c. Ask students: You tested what happens when objects with the same electrical charge are brought in contact and when electrical and neutral objects are brought together.  What do you think would happen when objects with opposite electric charges are brought together? Student answers will vary.  When two materials or objects with opposite charges are brought into close contact, the two objects attract each other.

2. Explain to students that when scientists design experiments, they perform an experiment in which nothing is done to the sample or nothing new is introduced.  This experiment is used to compare to the rest of the experiments and is called the control.  Encourage students to review the Trials they conducted.

a. Ask students: Which trials were the controls? Trials 1 and 4 were the controls.  The experiments were conducted without making a change to the balloon or the wool.

b. Ask students: How were the balloons and wool changed in the other trials? The wool and balloons were rubbed together before holding them over the arm, pepper, or other balloon.

c. Ask students: Why do you think performing a control was important? A control provides a comparison.  By placing the balloon and the wool over the arm without making a change to the balloon or the wool, students knew how the balloon and the wool affected the arm.  Students then altered the balloon and the wool by rubbing the wool over the balloon.  They held the altered balloon and the wool over the arm and again observed the effects of the wool and the balloon on the arm. By observing the difference between these two interactions, students determined that rubbing causes changes to occur.  Specifically, students found that rubbing the wool on the balloon caused both to be charged, and the hair on their arms was attracted to the charged balloon and charged wool. The same pattern holds true for the trials involving the pepper and the second balloon.  Observing the control allows students to make a comparison.

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F. To complete this Investigation, tell students they will continue to study another aspect of electricity, simple circuits, during the next Investigation.  One question they will explore is:  

Are there materials through which electrons can move more easily than others?