Pendulum Investigation

Transcription

1 During the first part of this investigation, you are going to explore how pendulums work. You can test things such as how the length of the string, the height of the drop or the weight of the bob effect the speed (number of swings) of the pendulum. Using what you learn, you will then design a Perfect 10 Pendulum one that makes 10 swings in 10 seconds. You will have materials to design models to test, and you will be asked to point out any strengths or weaknesses in your design. 1 of 17

2 Suggested Grade Span 6-8 Task During the first part of this investigation, you are going to explore how pendulums work. You can test things such as how the length of the string, the height of the drop or the weight of the bob effect the speed (number of swings) of the pendulum. Using what you learn, you will then design a Perfect 10 Pendulum one that makes 10 swings in 10 seconds. You will have materials to design models to test, and you will be asked to point out any strengths or weaknesses in your design. Big Ideas and Unifying Concepts Cause and effect Change and constancy Models Physical Science Concepts Motion and forces Properties of matter Mathematics Concepts Data collection, organization and analysis Graphs, tables and representation Measurement Time Required for the Task Two to three minute periods. (Two sessions may be needed for the first exploration to be completed. It is important that students be given ample time for each part of the inquiry.) Context Many commercially available science texts and activity kits have hands-on activities using pendulums; by the sixth grade, many students have probably already had some experience with them. Therefore, this assessment activity with pendulums can be easily used by uppergrade teachers to assess students ability to use the scientific method. (In other words, this 2 of 17

3 activity is more about assessing scientific investigation skills the ability to control and test variables one at a time and less about assessing knowledge of pendulums at this point in the teaching cycle.) This inquiry with pendulums is adapted from one of Piaget s classic experiments designed to probe the development of logical-deductive thinking in seven to 15 year-old children (Inhelder and Piaget, 1955). The purpose of this preteaching assessment activity is to assess the inquiry knowledge and skills that students already possess before the new teaching begins. Although no specific preteaching occurred to prepare students for this assessment activity (as it would in a culminating activity), this assessment makes it easy to see what skills of investigation students have already mastered over the year(s). Then, the teacher can identify what new teaching, reinforcement and practice should occur during future units of study. Students work in pairs to design and conduct their investigations. Each individual student is then responsible for completing an individual lab book stating the hypothesis, describing the design, organizing the data collected and stating conclusions. This activity also stresses two important aspects of cooperative learning: students work together to design and conduct the investigation (positive interdependence), but each student has the individual responsibility to articulate what s/he has learned from the activity (individual accountability). What the Task Accomplishes This investigation task is an excellent introduction to the scientific method and scientific inquiry. It allows the teacher to assess scientific literacy what knowledge and skills related to scientific exploration students have already acquired. All aspects of the scientific method are included in this activity: testing an hypothesis, designing an investigation and controlling variables, collecting and recording data, organizing data into a graphic representation, analyzing data to draw conclusions and using data to challenge misconceptions and raise new questions. Because there are several possible variables that could be tested, this activity allows the teacher to see which students are able to understand the need to isolate variables and test them independently. Additionally, this task emphasizes that mathematics and design are essential to conducting scientific inquiry. How the Student Will Investigate Begin by assigning roles to cooperative, two-member teams: principal investigator/materials manager and recorder/reporter. (See team worksheet on page 10.) For this activity, I combine four roles into two, placing a higher accountability and engagement level on each individual student for completing the inquiry task. After clarifying the information on the team worksheet, students work in pairs to complete the task. Students should be encouraged to first make some pendulums and explore how they work. A swing is defined as the distance traveled in one direction. Demonstrate for students what a swing looks like. (When the pendulum begins to swing back the other way, it is counted as a second swing. ) Be sure that all students can make a pendulum, count the swings and keep track of counting seconds during this initial exploratory session. 3 of 17

4 After about 20 minutes, discuss with students that they will be testing their predictions about some of the variables that affect the number of swings. To prepare them for writing a testable question/hypothesis, ask them to discuss whether they think that changing the weight of the bob will change the number of swings in 10 seconds. Also ask whether they think changing the length of the string will change the number of swings in 10 seconds. Ask whether there are other variables that might affect the number of swings. (You may wish to write some of the theories generated on the board.) Remind them to think about the things they have just done with their pendulums. Direct pairs of students to write a testable question and a plan for testing it. Remind them to record all data and observations. (Students may need up to 30 minutes to complete this part of the task.) The design of the Perfect 10 Pendulum is the final part to this inquiry. Students should use their data from the previous explorations to create a pendulum that makes 10 swings in 10 seconds. They should record all data and note any changes/modifications in their designs. Questions for the lab report are listed in the "Teaching Tips and Guiding Questions" section. A word about cooperative investigation groups: Begin by assigning roles and defining the inquiry task with clearly stated outcomes. A general rule of thumb in planning an inquiry task for cooperative groups is to determine the number of members in a group by the number of necessary roles for completing the task. There is nothing worse than having too little for each team member to do. I also structure the task so that a bit less time is given at the start than I think the teams will need. This forces teams to immediately get organized for the task. Then, I move about the room, checking on progress. We have a rule, ask three before me, which translates to, Do not ask the teacher what you are supposed to be doing unless you ask three other students first. Usually the easier questions can be answered quickly this way, keeping procedural questions to a minimum and maximizing use of teacher time for more important interventions during the inquiry lesson. Materials can be stored in a central location in the classroom or at each lab table, depending on your classroom set-up. Generally, I prefer to place the responsibility on students for gathering and returning the equipment they will need for investigations, rather than using my time to prepare and count all materials they will need. (Of course, there are exceptions especially when special preparation of materials or potentially hazardous materials are being used during investigations.) Interdisciplinary Links and Extensions General Extensions Find examples of pendulums (such as swings on the playground) and try some new investigations. Can you build a scale model of a much larger pendulum? Try to design a Perfect 6 or a Perfect 5 pendulum. Can you write a general rule about the relationship between the length of the string and the number of swings? 4 of 17

5 Science This activity could also be used as part of an end-of-year science portfolio assessment to determine the skills related to the scientific method that students have acquired at this point in their science education. Students could also be asked to review another student s lab book and assess whether or not the investigation could be repeated using only the descriptions of the experimental design and data provided in the lab book. Are the measurements of the lengths of the strings included? Is it clear how many trials were conducted? Are units of measure labeled? Is there a drawing to clarify the design? Since real scientists review their colleagues findings using a similar critiquing process, it demonstrates to students that their work is valued in the school s scientific community. Information Technology Students with access to the Internet might want to publish the results of future scientific investigations, inviting other students across the globe for critical response and verification of their results. This expands the scientific community and might also invite professional scientists to act as mentors to your students. Teaching Tips and Guiding Questions During the early exploration activities, teachers should move about the room observing and assisting or demonstrating when necessary. During the final part of the task, teachers should not provide guidance other than the questions for the report. Questions for the lab report could include: What is your hypothesis (or prediction)? What is your testable question? What is your plan for testing your hypothesis? What will you test? What data did you collect? What did you observe? What did you modify? What are your conclusions? What did you learn about the effects of changing the weight of the bob or the length of the string? Can you support your conclusions (give examples) using your data? Were you able to design a Perfect 10 Pendulum? How did you go about it? What have you learned about scientific investigation? about pendulums? What do you still wonder about? Concepts to be Assessed (Unifying concepts/big ideas and science concepts to be assessed using the Science Exemplars Rubric under the criterion: Science Concepts and Related Content) Scientific Method: Students determine the patterns and/or which kinds of change are happening by making a graph or table of measurements (change and constancy). Students observe and explain reactions when variables are controlled (cause and effect). Students see that how a model works after changes are made to it may suggest how the real thing would work if the same thing were done to it and that choosing a useful model (not too simple, not too 5 of 17

6 complex) to explore concepts encourages insightful and creative thinking in science, mathematics and engineering (models). Physical Science Properties of Matter: Students observe and compare physical properties of matter. Physical Science Motion and Forces: Students observe and compare that an unbalanced force acting on an object changes its speed or path of motion or both. Mathematics: Students use tables and graphs to show how values of one variable are related (increase, decrease, etc.) to values of another. Students understand that using numerical data and (precise) measurements in describing events, answering questions, providing evidence for scientific explanations and challenging misconceptions can be essential to scientific inquiry. Skills to be Developed (Science process skills to be assessed using the Science Exemplars Rubric under the criteria: Scientific Procedures and Reasoning Strategies, and Scientific Communication Using Data) Scientific Method: Observing, predicting/hypothesizing, designing an investigation, measuring, controlling variables, collecting and recording data, organizing data into a graphic representation, analyzing data to identify relationships and draw conclusions, communicating findings, challenging misconceptions and raising new questions. Other Science Standards and Concepts Addressed: Scientific Method: Students describe, predict, investigate and explain phenomena. Scientific Theory: Students look for evidence that explains why things happen and modify explanations when new observations are made. Scientific Tools: Students use measuring devices (measuring tapes, timers) to gather data. Physical Science Properties of Matter: Students observe, describe and compare objects and materials according to similarities and differences of their physical properties Physical Science Forces and Motion: Students identify and describe an unbalanced force acting on an object to change its speed or path of motion. Mathematics: Students use measurement and use tables and graphs to show how variables are related. Suggested Materials This activity requires little advanced preparation and minimal materials for the inquiry task to be carried out successfully. Pendulums can be made using inexpensive metal washers of several 6 of 17

7 (at least three) sizes, paper clips and string cut to different lengths. (Some students used dental floss instead of string for this task.) Rulers, tape measures or yardsticks are necessary for measuring the length of the strings. Masking tape, scissors and a timer (stopwatches or large wall clocks with visible second hands) are also needed. Students should have notebooks (lab books) in which to record data and draw their designs. Students can swing pendulums freely or tape a pencil to the edge of a desk so that the pendulum can hang from it and swing freely. Another possibility is to bend a coat hanger and either tape it to a desk edge or close it in a desk or drawer so that the curved hook at the top of hanger acts as a hanger for the pendulum to swing from. Refer to the worksheet on page 10. Possible Solutions Students should be able to determine that the length of the string will affect the number of swings. The weight of the bob will NOT affect the number of swings. (This is a very difficult misconception to overcome for many students even when the data refute it! See Practitioner example for discussion of experimental error.) Students solutions should demonstrate the following skills: Stating a hypothesis (or testable question) as a cause-effect relationship Designing an investigation and building a model to test the question Controlling one variable at a time and indicating the number of trials Using tools to measure and record data with appropriate units of measure labeled Using a graph or table to represent data Using data as evidence and applying logic to support conclusions Task-Specific Assessment Notes Novice The student has little understanding of the inquiry process and the importance of testing one variable at a time. Both the length of the string and the weight of the bob were tested at the same time in a guess-and-check process. The student participated in exploration but did not record data in an organized manner. It appears that either only one trial was completed or only data for one trial were recorded. Conclusions are not supported by data. The student does not discuss procedures used. What this Novice investigator needs next: Guided practice in collecting data for at least the first part of the investigation, until s/he shows understanding of a clear purpose for what s/he is doing. Chart to fill in which suggests the number of trials to perform while testing only one variable. Reminders along the way about what question s/he is testing, what data s/he is gathering, why s/he needs to write or draw, etc. Short list of related science words (collaboratively built with a partner or teacher) that will help him/her to talk about what s/he is doing. (variable, data, length, etc.) Some clear models of what the Apprentice level looks like. 7 of 17

8 Apprentice The student states a hypothesis as a cause-effect relationship and understands that during inquiry and exploration, some variables must remain constant. The plan for testing the (two) hypotheses varies both the length of the string and the weight of the bob, first testing a long string with three different weights, then a short string with three different weights. Although the student states two different hypotheses, s/he only tests the effects of the weight. In the exploration, s/he uses appropriate tools to gather data, but lacks the skills to organize it into a chart for easier analysis. While the student successfully completed the task of finding a Perfect 10 Pendulum, s/he never used data to identify the pattern that the weight made no difference. The student did not measure and record the length of the string, yet his/her conclusions refer to the effects of the length of the string. S/he may have just been lucky in completing the task! What this Apprentice investigator needs next: Checklist for seeing how the plan connects to the testing of each hypothesis and to the stated conclusions. Reminder to measure and record such things as length of string so that someone else can repeat his/her tests. Assistance in creating a graphic organizer/chart to put his/her data in. Assistance and demonstrations in looking for patterns in the data in the charts. Clear models/descriptions of what the Practitioner level would look like. Practitioner The student states two hypotheses as cause-effect relationships and understands that during inquiry and exploration some variables must remain constant. The plans for testing the (two) hypotheses are well-organized and the reader can follow them through to each set of conclusions. Variables are identified and tested separately in the investigation. Appropriate tools are used to gather data for six trials. Data are recorded accurately. Conclusions are clearly supported by data, yet the first conclusion is not accurate. The student records minimal differences in the number of swings with different weights and interprets it as a cause-effect relationship. (This is typical at this age and opens the door for new teaching opportunities. See below.) What this Practitioner investigator needs next: Guidance in assessing his progress with peers and for himself or herself. Guidance in how to check the accuracy of his/her data and understanding the concept of experimental error when errors are within reasonable expectations and do not indicate significant results or changes. (The student should complete more trials than three to begin to see a definite pattern, or the class could compile all of their data into one comprehensive chart to look for trends.) Examples of more complex ways to organize and represent data. Clear models/descriptions of what the Expert level would look like. 8 of 17

9 Expert The student states two hypotheses as cause-effect relationships and understands that during inquiry and exploration some variables must remain constant. The plan for testing the (two) hypotheses is not as well organized as the plan at the Practitioner Level but does discuss the general procedures to be used. The reader can clearly see a connection between each hypothesis and each conclusion. Variables are identified and tested separately in the investigation. Appropriate tools are used to gather data for 12 trials. Data are recorded accurately and organized in a chart. Conclusions are clearly supported by data. What this Expert investigator needs next: Guidance in assessing his/her progress with peers and for himself or herself. Guidance in how to check the accuracy of data and understanding the concept of experimental error when errors are within reasonable expectations and do not indicate significant results or changes. Examples of more complex or electronic ways to organize and represent data. Clear models/descriptions of what other Expert level work looks like. 9 of 17

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11 Novice 11 of 17

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14 Practitioner 14 of 17

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16 Expert 16 of 17

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