Electrostatics: Charging Objects by Friction

Transcription

1 Physical Science 8 Electrostatics: Charging Objects by Friction Relevant SOL(s): PS 1 a) chemicals and equipment are used safely; f) independent and dependent variables, constants, controls, and repeated trials are identified; j) valid conclusions are made after analyzing data; n) current applications of physical science concepts are used PS 3 a) the contributions of Dalton, Thomson, Rutherford, and Bohr in understanding the atom b) the modern model of atomic structure PS 4 b) classification of elements as metals, metalloids, and nonmetals PS 11a) static electricity Instructional Objectives: SWBT Explain how electrons transfer and effect the charge of an object SWBT Describe how electrical forces relate to attraction and repulsion SWBT Describe how a neutral object becomes polarized Lesson Segment & Time Est. 1 class period 50 min Introduction Predict and Explain Materials Instructional Sequence Teacher/Student Actions 5 minutes Introduction to Electrostatics: Wandarama and the butterflies, pie tins As students enter classroom, demonstrate the metal butterflies and mini pie tins that react in the presence of the Wandarama wand. What is happening? 15 minutes PowerPoint 8 slides (5 minutes) Static electricity simulation from PhET balloons-andstatic-electricity (5 minutes) Check for prior knowledge: Brief review of atomic model, particle properties, charges, and how subatomic particles interact Show 8 static digital visualizations and ask students to answer questions. Name the parts and locations of subatomic particles. What is charging by friction? What charges in the atom could account for this behavior scene on slide1? Explain the rule of attraction/ repulsion. What is polarization? What is the difference in a charged object and a polarized object? What is polarization? Introduce static electricity PhET. Demonstrate the simulation without the charges showing. Ask students to predict what happens when balloon is rubbed on sweater. Demonstrate its use with the sweater. Ask students to predict what happens with same balloon use on wall. Demonstrate its use with wall. Repeat each with charges showing and ask students to explain. Can the charged particles assist in describing the how the scenarios are alike or different? Teacher leads students in a brief Q & A of PowerPoint and PhET simulation Intent is to introduce difference between charged objects and polarized, neutral objects 1

2 Lesson Segment & Time Est. 1 class period 50 min Materials Instructional Sequence Teacher/Student Actions Body (Observe) (Explain) 25 minutes Lab equipment: acrylic and Teflon rods, silk cloth, small paper circles, salt, pepper, paper, clear plastic ruler, Petri Dish empty soda cans, balloons Students will complete 3 short laboratory exercises upon completion of their entry ticket w/s. Brief pre-lab (5) minute discussion of materials and procedures for each activity. Students will work in heterogeneous assigned teams and report to their stations where supplies and materials are available to complete each activity, Predict: Students will make predictions on each lab write-up before completing procedures and analyzing results. Observe: After predictions, students follow procedures and make observations, collect and analyze data/results. Each student completes individual lab activity, worksheet. Each student will submit completed lab sheets following brief, whole class post-lab discussions. Teacher will lead a pre-lab discussion of materials, procedures, and rotations Teacher will circulate lab stations and check for data recording, students understanding, comprehension, and explanations Explain: Upon completion of student investigations, teacher will lead a whole group discussion of results, findings, and explanations. Students share findings and explanations in class discussion Closure (Explain, cont.) 10 minutes Total Time = 50 minutes 10 minutes Use of remaining 3 slides from lesson introductions plus 2 additional static visualizations Post lab discussion will incorporate vocabulary review of atomic model, atomic particle properties, charges, and interactions; vocabulary reinforcement of lesson terms, electrostatic forces, charged objects, friction, and polarization. Introduction to new vocabulary related to the process of charging objects: the triboelectric series, charging objects through conduction, and induction, and Van de Graaff generators (static visualizations used in post lab discussion) Students will discuss and share out findings before final conclusions on lab papers are written. Scaffolding of final conclusions writing provided for SPED students Assessment Plan: Collect lab papers of each student s predictions, observations, and explanations. Grade and use as a formative assessment Allow students to play with Wandarama as intro to the Van de Graaff generator for next lesson, time permitting 2

3 Activity 1: Moving an Empty Can Name Date Class Can You Move a Can Without Touching It? Objective: Have you ever wished that you could pull an object toward yourself without touching it? In this activity, you will use static electricity and observe what happens when objects that are statically charged interact with each other. Materials: empty aluminum can balloon Prediction: 1. Can you move the empty can with the balloon and not allow either object to touch? 2. What atomic particles are involved in the process of moving the can without touching it? Explain your answer. Procedure/Observations 1. Place an empty aluminum can on its side on the lab table. 2. Blow up a balloon and tie it closed. Rub it back and forth on your clothes. 3. Hold the balloon 2 3 centimeters from the can. 4. Slowly move the balloon further away from the can. Describe you observations. 3

4 5. Move your balloon to the other side of the can and describe what happens. Explain: 1. Why do you think you were able to move the can after rubbing the balloon on your clothes? What parts of the atoms were involved in the process of moving the balloon? 4

5 Activity 2: Static Electricity with Salt and Pepper Materials: One teaspoon of Pepper One teaspoon of Salt A piece of Wool or Fake Fur Plastic petri dish, sheet of paper, plastic rod or ruler Prediction: 1. Predict how you can a separate a mixture of salt and pepper using a plastic ruler and a piece of cloth. 2. Predict how you can separate a mixture of salt and pepper using a plastic Petri Dish Procedure: Using a Sheet of Paper 1. Measure out one teaspoon full of salt and one teaspoon full of pepper onto the sheet of paper. 2. Use a pencil's eraser top or pen top to mix the salt and pepper together. 3. Take the plastic ruler/rod and rub it with the wool/fake fur. 4. Approach the pepper with the ruler/rod from above slowly. The pepper will begin to jump onto the ruler. As you get closer to the mixture, the salt will eventually begin to jump to the ruler. The pepper will jump to the ruler/rod and stick. Using a Petri Dish 1. Measure out one teaspoon full of salt and one teaspoon full of pepper into the petri dish. 2. Place the cover on the petri dish and mix well by gently swirling. 3. Rub the top of the petri dish with the fur. Turn the petri dish over for a few seconds and then turn it back to the original position. The pepper should stick to the top of the petri dish. 5

6 Explain: 1. What made the pepper stick to the cover of the petri dish or to your ruler/rod? 2. What effect did rubbing have on the petri dish or to the rod/ruler? 3. Why does the pepper jump to the rod/ruler before the salt? 4. Can you think of other ways to separate this mixture? 5. Why does the pepper only stick to the rubbed areas of the petri dish lid? 6

7 Activity 3: Investigating with charged rods and their reactions to paper dots and water PS 11 a Background In this laboratory investigation you will be using an acrylic and Teflon rod with a silk cloth. Rubbing the silk cloth on each rod will cause a charge transfer on the materials. The electrons transferred from rubbing are responsible for the charging. The protons in the atoms remain where they are and do not contribute to static electricity. Silk tends to attract loose electrons that may be on an acrylic rod and pull them off the acrylic when they are rubbed together. Teflon has a strong tendency to attract the loose electrons that may be on silk. Thus rubbing each rod with silk should result in a positively charged rod and a negatively charged rod that you will use to complete this activity. Materials: Acrylic rod Teflon rod silk Small paper dots from hole punch Small stream of water from faucet 1. Predict the charge each rod will become, positively charged or negatively charged, after being rubbed with silk. Explain your reasoning. 2. Predict how small, neutral pieces of paper will behave when a positively charged rod is brought near them. 3. Predict how a small, neutral pieces of paper will behave when a negatively charged rod is brought near them, 4. Predict how a small stream of water will behave when a positively or negatively charged rod is brought near the water. Procedure: 1. Make sure the Teflon rod is neutral by sliding it across the palm of your hand. Move the rod close to the paper. Describe the behavior of the paper dots. 2. Rub the Teflon rod with the silk cloth by striking the rod against the silk cloth held hanging from your fingers. Move the rod towards the paper. Describe the behavior of the paper dots. 7

8 3. Make sure the acrylic rod is neutral by sliding it across the palm of your hand. Move the rod close to the paper. Describe the behavior of the paper dots. 4. Rub the acrylic rod with the silk cloth by rubbing it against the silk cloth held in the palm of your hand. You may need to rub the acrylic rod several times to charge. Move the rod towards the paper. Describe the behavior of the paper dots. 5. Repeat steps 1-4. Substitute a small stream of water for the paper. Describe the behavior of the stream of water. Try hot and cold water streams. Explain: 1. Why do you think the paper dots displayed the behavior that they did in step 2? 2. Explain the behavior of the paper dots in steps 2 and Explain the behavior of the stream of water in step Does the temperature of the water affect the results of the charged rods? 5. Explain the purpose of testing the neutral rods with paper dots and the water stream. 8

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10 Triboelectric Series static illustration: For use in post lab discussion, Activity 3. Explanation for why teflon rods and acrylics rods react differentyly with silk and charge oppositely. See question # 1 predict Cups and empty cola cans static illustration: For use with post lab discussion to assist students in understanding of aluminum can as a conductor that has become polarized. For use in Activity 1, Explain, question # 3 Lead into next topic: charging by conduction and induction 10