Effect of Fulcrums on a Lever

Transcription

1 After exploring levers, you now have some ideas about how the position of the fulcrum affects the amount of effort needed to lift a load. Using a ruler (as a lever), a pencil (as a fulcrum) and 10 pennies (as your load), investigate to find out which position of the fulcrum makes it easiest to lift the 10 pennies. You will need to make a prediction: Where on the lever/ruler does it make it easier to lift (least amount of pennies used to lift the 10 pennies on the other side)? Draw a labeled picture of your prediction: What does this model look like? What is your hypothesis? Test the possible positions and record your results in an organized way. Draw a labeled picture of what worked, and state some conclusions about the position of the fulcrum and about the effort applied. 1 of 13

2 Suggested Grade Span 3 5 Task After exploring levers, you now have some ideas about how the position of the fulcrum affects the amount of effort needed to lift a load. Using a ruler (as a lever), a pencil (as a fulcrum) and 10 pennies (as your load), investigate to find out which position of the fulcrum makes it easiest to lift the 10 pennies. You will need to make a prediction: Where on the lever/ruler does it make it easier to lift (least amount of pennies used to lift the 10 pennies on the other side)? Draw a labeled picture of your prediction: What does this model look like? What is your hypothesis? Test the possible positions and record your results in an organized way. Draw a labeled picture of what worked, and state some conclusions about the position of the fulcrum and about the effort applied. Big Ideas and Unifying Concepts Cause and effect Models Systems Physical Science Concepts Motion and forces Transfer and transformation of energy Mathematics Concepts Comparison of attributes or effects Data collection, organization and analysis Graphs, tables and representations Measurement Time Required for the Task Approximately two 45-minute sessions. 2 of 13

3 Context This is one of several introductory investigation tasks in a unit on simple machines. Students previously have investigated a number of concepts around this topic. In groups, students explored a number of everyday machines, such as blenders, vacuums, telephones, etc., by taking them apart to see how they work. They created a human machine to perform a specific work task and looked at how machines are systems with inputs and outputs. They explored levers using rulers, pencils, and pennies and came to a number of ideas about levers and work. We investigated levers using a life-sized seesaw with students as the load. Using the above ideas, as well as their prior knowledge and experience, students will control the variables of position of fulcrum and load (ten pennies) to see if their predictions about the position of the fulcrum are correct. What the Task Accomplishes This task is one of a number of guided investigations about each of the six simple machines. It is used to teach and reinforce the idea that simple machines make work easier. In this task, students will learn that the closer the fulcrum is to the load, the easier the work is (in other words, less effort is needed). It also reinforces many science process skills, such as making predictions and hypotheses, collecting and recording data, and drawing conclusions that reflect concepts learned. How the Student Will Investigate After the initial explorations of levers, we discuss as a class some possible ideas about how to make the work of the lever easier. This leads to exploring changes in the location/position of the fulcrum. We also use relevant vocabulary (load, effort, work, fulcrum) during these discussions. Students then write their testable question and make a prediction about where the position of fulcrum will make the effort easiest. Students will need to decide how they will test this and how they will record the data they collect. Students will use the materials to test their idea about work and levers and then draw conclusions based on what they learned during their investigation. Interdisciplinary Links and Extensions Science There are a number of related activities with levers that students can do. Using the life-sized seesaw (using a board as the lever), students can investigate lifting a variety of objects as well as moving the fulcrum to explore its relationship to effort. Students can also look for levers that are used in everyday life and explore how levers utilize a fulcrum s position to make work easier. Students can also investigate second- and third- class levers such as wheelbarrows and brooms and the work that these do. Finally, students can discuss the saying from Archimedes, If I had a place to stand and a big enough lever, I could move the world. 3 of 13

4 Social Studies Students can research machines and tools, how they have changed over the years, and their impact on doing work in our lives. They can also research the invention or conception of different machines and simple machines and the people identified with these ideas. Technology Give students a number of design challenges where they need to use simple machines to do work. An example might be to move the teacher s desk to a new location or to lift a heavy rock off the ground. As a final activity in this unit, I have the students create a new machine that utilizes at least three of the simple machines to make some type of work easier for them to do. They can be as creative as they want to be. Mathematics Students do measuring and comparing of weights, lengths, and heights frequently during this activity as well as in later activities in this unit. The mathematical concept of scale could also be introduced in looking at sizes of machines and/or amounts of effort to lift significantly larger loads. Movement My students create a human machine each person as a separate part that is connected to the others and performs a different function in the machine to get the work done. We moved a heavy dictionary from one end of the room to the other. Teaching Tips and Guiding Questions Because this is an introductory investigation, it will be important to make sure that students have some understanding of the purpose of the fulcrum and have some ideas about how its position can affect work being done. Discussing the students ideas beforehand can help focus their thinking and ensure that they are on the right track during the investigation. Some helpful questions to ask might be: Where is the fulcrum? the lever? the load? What is the purpose of the fulcrum? What does it do? What are the variables that will be controlled during this investigation? What will be changed? How will you record the changes? How does moving the fulcrum affect the effort (number of pennies) needed to lift the ten pennies on the other side? How will you organize your testing and your results so they tell you something? Why does this position make the work easier? Harder? What ideas do you have about why this is happening? What conclusions can you draw about effort and position of the fulcrum? 4 of 13

5 Concepts to be Assessed (Unifying concepts/big ideas and science concepts to be assessed using the Exemplars Science Rubric under the criterion: Science Concepts and Related Content) Physical Science Transfer and Transformation of Energy: Students understand that energy is a property of many substances, that it is associated with mechanical motion and that a simple machine uses energy (effort) to do work. Physical Science Motion and Forces: Students explain that a lever is a system; its input is the effort needed and the output is the work done (the lifting). Students explain that work is defined as moving an object from one place to another and that by moving the fulcrum (a part of the system) you change the amount of effort needed to do the work. Students use the terms lever, fulcrum, load and work appropriately and describe cause-effect relationships with some justification, using data and prior knowledge. Scientific Method: Students observe and explain reactions when variables are controlled. 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 is done to it. Mathematics: Students use tables and graphs to show how values of one variable are related (increase, decrease, etc.) to values of another. They use numerical data and (precise) measurements in describing events, answering questions, providing evidence for scientific explanations and challenging misconceptions. Skills to be Developed (Science process skills to be assessed using the Exemplars Science Rubric under the criteria: Scientific Procedures and Reasoning Strategies, and Scientific Communication Using Data) Scientific Method: Observing, predicting and hypothesizing, drawing and labeling diagrams, collecting and recording data, challenging misconceptions, raising new questions and drawing conclusions to communicate learning. Other Science Standards and Concepts Addressed Scientific Method: Students explain and communicate phenomena. Students control variables. Scientific Theory: Students look for evidence that explains why things happen and construct an explanation based on their observations and the concepts they have learned. 5 of 13

6 Physical Science Motion and Forces; Transfer and Transformation of Energy: Students can explain that energy is a property of many substances, that it is associated with heat, light, electricity, mechanical motion, sound, nuclei and the nature of a chemical and that it is transferred in many ways. Suggested Materials I supply rulers (either plastic or wood), pennies (enough so that students have 10 for the load and at least 20 others for testing), and pencils to use as fulcrums. Other classroom objects would also work well. Possible Solutions A correct solution will include the observation that the closer the fulcrum is to the load, the easier the effort or work is. Students should also include the testable question, a prediction and/or hypothesis, a labeled drawing of their prediction and the position that was successful, test results that are organized (in a graph or table), and conclusions that accurately reflect data collected and what was learned. Students should use appropriate vocabulary in their explanations. Task-Specific Assessment Notes Novice This student includes the testable question and a drawing of his/her prediction, although the prediction is not clearly stated. The test results are organized and labeled but are incomplete not all positions were tested and recorded. There is a drawing of the position that was easiest, but it is not clearly labeled as such. The student includes a somewhat correct conclusion, but it is lacking detail and use of appropriate scientific vocabulary. Apprentice This student includes a testable question and a drawing of his/her prediction. The prediction, however, is not written out, but it is fairly clear in the drawing and indicates what ideas this student has about levers and fulcrums. The test results are complete but are not labeled as they should be (effort = number of pennies and position = placement of the fulcrum). Data are not organized so that a clear pattern can be seen. The student s drawing of what worked the best is clear, and the conclusion, while brief, demonstrates some conceptual understanding and use of some appropriate vocabulary. Drawings should have shown pennies as the load and effort (not, e.g., 16 tons and 5 lbs ) and also should have included numbers on the ruler. Practitioner This student includes the testable question. S/he states a prediction and hypothesis. The drawing is well-labeled and detailed. The test results are complete, organized and well-labeled. There is a well-labeled drawing of what worked the best; it clearly shows what was learned. The student s conclusions demonstrate understanding of the concepts and indicate appropriate use of vocabulary. This student also begins to make some connections as to why the fulcrum works 6 of 13

7 better when closer to the load by stating, The closer the fulcrum is to the load the more the lever does the work. Expert This student includes the testable question. S/he includes a prediction and hypothesis. The drawing of the prediction is very clear and well-labeled, indicating good overall understanding of the concepts. The results are clearly labeled, well-organized and complete. There is a drawing that again is well-labeled, showing the position that worked the best (same as his/her prediction). The conclusions are complete and detailed. They indicate good understanding of the concepts and use of appropriate vocabulary. This student also makes connections, extends thinking as to why this might be true, and clearly explains his/her ideas. 7 of 13

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