Fair Tests: Learn About Liquids

Transcription

1 During this investigation, you will explore any question you have about liquids. Using what you already know and have observed related to density, viscosity and surface tension in liquids, your team will make a prediction, consider the variables and materials involved, and conduct your test. Be sure to test only one variable and to determine how you will control the other variables (keep them the same) during this investigation. Plan how you will test your question and record your results in an organized way. Decide what tools you need to measure or collect data. Your conclusions should refer back to the data you collected and discuss whether your prediction was accurate. On a poster, your group will share any new concepts you have learned from your results. 1 of 18

2 Suggested Grade Span 3 5 Task During this investigation, you will explore any question you have about liquids. Using what you already know and have observed related to density, viscosity and surface tension in liquids, your team will make a prediction, consider the variables and materials involved, and conduct your test. Be sure to test only one variable and to determine how you will control the other variables (keep them the same) during this investigation. Plan how you will test your question and record your results in an organized way. Decide what tools you need to measure or collect data. Your conclusions should refer back to the data you collected and discuss whether your prediction was accurate. On a poster, your group will share any new concepts you have learned from your results. Big Ideas and Unifying Concepts Cause and effect Models Physical Science Concept Properties of matter Mathematics Concepts Data collection, organization and analysis Diagrams Measurement Time Required for the Task Approximately two to three class sessions (after demonstrations). Context These fair-test investigations followed almost a week of explorations. Several teacher demonstrations and guided small group activities introduced the concepts of density, surface 2 of 18

3 tension and viscosity (or laziness as we called it) in liquids. We did about 2-3 activities for each concept, including: A demonstration, placing raisins in clear soda. Students observed that at first, the raisins sank; then bubbles began to attach to the bumpy surfaces, causing the raisins to rise; and at the surface the bubbles burst, and raisins sank again. We discussed where the gases came from and went to and also that the density of the raisins changed with and without bubbles attached causing them to rise (when less dense than water) or sink (when more dense than water). Observing how a cardboard boat floated and moved on water, before and after adding dishwashing detergent (which changes the surface tension of the water). When we did it, the boat suddenly moved across the water when soap was added. Observing paper clips staying on the surface of water when only a few were placed there (observing surface tension and meniscuses the curved surface of a column of liquid). Students were then guided to suggest some testable questions to explore further. I suggested that they use the phrase, What would happen if... to begin to extend their thinking. Small groups of students looked at the ideas each individual in the groups had generated and decided on a question for the group as a whole to explore as a fair test. What the Task Accomplishes This investigation demonstrates a number of things. It enables students to practice designing investigations, generating their own testable questions. It also demonstrates whether they understand the idea of fair testing and controlling simple variables. Students also continue to use and practice a number of science skills, such as observing, predicting, testing ideas, using materials and tools, and drawing conclusions based on their observations and test results. Students communicate findings and use their results to raise new questions to explore further. The idea of fair testing and controlling variables is a difficult one. This task is part of ongoing instruction in testing one variable at a time, measuring same amounts for each test, and relating results back to the original question being tested. Additionally, I wanted to stress that while the earlier observations that we have done were important, recording detailed observations and using measuring devices to collect more precise data were the next steps in improving our investigation process. How the Student Will Investigate After the earlier class investigations already described, students were encouraged to explore their own questions. The idea of fair testing was reviewed and led to students making decisions and planning their investigations. I held conferences with groups of students at each step (after choosing their question and making their prediction, after deciding on a process and materials, etc.) to be sure that they were clear before going on. Students worked in small groups and had access to different types of containers, household liquids (water, syrup, food coloring, dish liquid, etc.) and various measuring devices, such as stop watches. Students needed to decide what materials would be needed, how to measure or 3 of 18

4 control amounts, and what process to use as they tested. They stated a testable question, made a hypothesis/prediction based on their understanding, listed materials to be used, described procedures to be followed, and collected data. Interdisciplinary Links and Extensions Science/Mathematics Many students will raise new questions through these investigations. This can be an opportunity to extend conceptual understanding of the properties of liquids and also introduce taking more precise measurements as part of the data collection. By this age, students can begin to use scales, stopwatches, and metric and standard measures for weight and volume, etc. with confidence. Small groups could explore further fair testing with density (the relationship between mass and volume that causes something to float or sink), surface tension (the property of a liquid that makes it behave as if its surface has an elastic skin) and viscosity (the measure of the resistance of a liquid/fluid to flow: e.g., Is warm syrup more lazy than cold syrup? ). Note: In water, surface tension is very strong due to intermolecular hydrogen bonding and it is responsible for bubbles, drops, meniscuses (the curved surface of a column of liquid) and capillary action (rising of water in a tube, ability of a liquid to wet a surface or be absorbed by a porous substance. Have students test the wetting properties of various liquids and substrates or absorption rates of different materials. Teaching Tips and Guiding Questions If students are new to fair tests and controlling variables they will need assistance identifying possible variables. Sharing possible testable questions as a whole class enables students to hear a variety of ideas before deciding the variables they will test. Students may need some help planning how to test their variable, deciding how and what to measure, and organizing their data. (Editor's Note: See the Exemplars Teacher s Toolkit on this CD for some ideas for giving students feedback to guide their fair tests.) It s helpful to provide students with models of different charts, tables and graphs (bar, scatter plot, stem and leaf, etc.), appropriately labeled using science and mathematics vocabulary. As students begin their testing, consider asking these questions to guide their thinking: What is it you want to find out? What is your prediction? Does your prediction tell what you think will happen? (cause-effect) Why do you think that will happen? What have you observed before that helped you make this prediction? Is this is a fair test? What are you changing? What is staying the same? What materials will you need? What will you measure? 4 of 18

5 What tools will you need? Did you have to modify your experiment at any point? What are your conclusions? How did you use your data to get your conclusions? Did you explain your procedure clearly enough so that others can understand and perhaps repeat what you did? Can you support your conclusion using evidence from your results? Have you used any science or mathematics terms to describe what you observed or learned? (solid, liquid, gas, expand, variable, length, etc.) What new ideas do you now have? Do you have a new question to test? Note: Remind students along the way that it is not important whether their prediction is correct, but that they can use data and observations to justify or refute their prediction. This is what scientists do! 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) Physical Science Properties of Matter: Students observe and compare physical properties of matter. Students need to be able to use the terms or apply the concepts of surface tension, density and viscosity appropriately and be able to describe cause-effect relationships with some justification, using data and prior knowledge. Scientific Method: 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 complex) to explore concepts encourages insightful and creative thinking in science, mathematics and engineering (models). Mathematics: Students understand that representing and analyzing data appropriately, identifying trends and patterns and using numerical data and precise measurements in describing events, answering questions, providing evidence for explanations and challenging misconceptions are important in 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: Using prior knowledge, using scientific reasoning, comparing, inferring, predicting, observing, controlling variables, testing ideas, measuring, collecting and representing data, drawing conclusions based upon results and communicating what was learned. 5 of 18

6 Other Science Standards and Concepts Addressed Scientific Method: Students describe, predict, investigate and explain phenomena. Students control variables. Scientific Theory: Students look for evidence that explains why things happen and modify explanations when new observations are made. Physical Science Properties of Matter: Students describe and sort objects and materials according to observations of similarities and differences of physical properties. Suggested Materials Students used a simple planning guide as they worked to design their investigations. Groups had access to different types of containers, household liquids (water, syrup, dish liquid, etc.), various objects and measuring devices, such as stopwatches, and materials brought from home. Planning investigations over several days allows time to gather materials needed for the testing. Students were provided with poster paper, markers, glue, etc., for drawing diagrams to explain their experiments and for the final poster presentations. Some students also typed some of their information, using school computers. Possible Solutions All information is presented on a poster to share with the class. This should include: a testable question; a hypothesis showing a cause-effect relationship ( when I do this, this is what will happen ); materials used; procedures followed, including variables to be controlled/variables tested; data presented in an organized, clear way; and conclusions supported by data. Drawings may also be included and should be labeled. Conclusions should refer back to data collected and should discuss whether the prediction was accurate. A new question might be raised. Task-Specific Assessment Notes Novice These students complete the task. A testable question is stated, yet the hypothesis appears to be more like random guessing than based on prior knowledge. Procedures are incomplete and show little evidence of understanding fair testing. There is no reason given for having two jars in the investigation and no mention that the drops of soap are to be the same each time. The data collected are linked to conclusions made; however, there is no additional explanation as to why three drops made the clip sink. Apprentice These students complete the task and provide a labeled drawing to explain what happened. A testable question is stated, yet the hypothesis does not appear to be based on prior knowledge. 6 of 18

7 Procedures are for the most part complete, although the students do not say how clips will be put on the water (one at a time, etc.). There is limited evidence of understanding fair testing. The data collected are linked to conclusions made, and there is an attempt to provide additional explanation and interpretation. A logical new question, based on results, is raised showing evidence of scientific reasoning. Practitioner These students state a testable question linked to the concept of surface tension and make a prediction based on prior knowledge and experience. Drawings are labeled and clearly show each step. Procedures are complete and show evidence of understanding fair tests. Data are collected and recorded. Conclusions are clear and refer to data and observations made. Expert (I have rated this Expert, mainly due to the precision in collecting, organizing, and displaying data for the task.) The student states a testable question related to viscosity. The prediction appears to be based on previous knowledge and experience. Procedures and explanations show how each liquid will be tested. The student shows understanding of fair testing by using the same amounts of liquids, timing each one going the same distance (to a finish line) and recording results. Data are collected using a stopwatch. A table is used to organize and display data. Labels make the table clear as to what was collected and represents accurately and effectively what the students did during the investigation. Conclusions refer to data and observations made. A new question is raised. 7 of 18

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