- Students will experience science as a way of understanding and explaining based on evidence and argument.
- Students will develop and test their ideas about air pressure and vacuums by doing investigations into movement of fluids in tubes.
- Students will relate their experiences and ideas to the historicalinvestigations concerning the existence of vacuums and the role of air pressue in the movement of liquids in tubes.
In the history of science, the some of the most intense and fruitful investigations have been about understanding common events. For example, understanding the "rising" and "setting" of the sun and moon or the paths of falling objects caused a great deal of scientific inquiry. To fully explain many of these common events, you must be able to conceptualize something that may contradict your direct experience or is beyond your perceptual abilities.
To accept the heliocentric world view necessitates that you must accept an idea that is not apparent from direct experience. We all see the sun "rise" and "set". The simplest explanation is that the world is stationary and the stars and planets revolve around the Earth. This explanation is also wrong. The better explanation is hidden in the fact that we can not directly sense the speed and relative motion of the Earth as it rotates and
revolves around the sun.
The problem associated with understanding the effect of air pressure is the relative difficulty in perceiving that air has weight or that is actually exists. Air is colorless, tasteless, and extremely light. It's presence is so common that we take it for granted unless you are submerged in water or in a tornado. The awareness of air itself, not to mention the pressure it exerts, is not readily apparent in our daily experience. Think about how many times you have described a glass NOT FILLED with water or some other fluid as being EMPTY! If you don't perceive the existence of a substance it is impossible to use it to explain phenomenon that you experience.
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Introudce Behavior of Fluids Ideas and Historical Apporach.
Science as a process to explain and understand things based on observation and evidence has been the standard definition in my science class. I inform students of my belief that when students are asked to learn science concepts in class they are retracing similar steps that great science minds have taken to understand phenomenon. Basically, we ask them to learn something that could have taken hundreds or thousands of years to understand in a matter of days. In science class, we compress and simplify the time and energy that was spent investigating how something works and present it to students as if it had no life of its own and disregard the human effort it takes to really understand something. Is it any wonder that science is seen as difficult, complex, confusing and just plain hard? The focus of this unit will be in phenomenom related to the behavior of fluids, meaning substances like water and also air that have the ability to flow.
Become aware of student concepts and knowledge.
Get baseline information on student concept of how water goes up a tube that you suck on. Demonstrate using blue food coloring in water and a long clear plastic tube. Ask students to explain as completely as possible to describe how water moves up the tube and down the tube or why it doesn't go up unless you do something to the tube. Ask them to provide a diagram to help show their ideas. Work in pairs and turn in a single piece of paper that best explains the phenomenon. The teacher should not use the words suck, suction, vacuum, pressure, etc. Your job is to perform the demo and make sure that students give complete descriptions. Collect data and review. Try to break down the basic concepts and ideas to help you understand them. Keep these ideas for later, when you try to put together the effect of air pressure on the behavior of liquids in tubes.
POINT TO MAKE.....Your ability to explain depends on the information, awareness and tools that you have to think with. Which explanation is CORRECT? Most all students will ask this question. ANSWER....There is no correct explanation.....Only better or more functional or more complete or detailed or logical or consistant. It depends on the tool box of ideas that each one brings to the task. Science is the attempt to explain the world around us and make it more understandable. The level at which you understand, question, and perceive depend on one another. The more you know, the better your questions and the more you notice.
Exploring the materials and event.
Explore and Record Observations, Infer, and Develop Theories about how different plastic bottles drain water and the factors that control the rate of draining.
Students are to work in pairs to explore, inquire, mess around, get to know the ways in which different plastic bottles drain water. All bottles have the same size whole in the bottom at approximately the same distance up from the bottom. The bigger the variety of sizes and shapes the better.
TASK: Record as many observations, measurements and inferences as you can about how water drains out the bottom. Make a list of factors that you think control the rate of flow of water out of the containers. Be prepared to report your findings in a class discussion.
Note.....If your room is not equipped with a mop and bucket get one. This activity will provide some good reason to clean that dirty floor of yours.
Class discussion and record of observations, inferences, and factors controlling the rate of water flow.
Use a large piece of paper to record student observation and ideas. This should be a time where any and all comments are recorded. Focus should be on info collected on rate of flow and length of stream. Under what conditions did the rate change or length of stream change? Is the rate of flow constant? Measurements of flow rate. The observations should be descriptions of what happened. The facts of the event.
On the same piece of paper, Refer to the observations and let students put together the inferences about the relationship between volume and flow rate, flow rate and length of stream, pressure and flow rate, pressure and length of stream, volume and pressure, weight of water and pressure, etc. The inferences should be logical conclusions based on the observations made. Make a list of all the possible factors that did or could effect the flow rate or length of stream of water (all of which would indicate a change in pressure).
Find a Focus Question and Design an Experiment.
Students are to pick one of the factors discussed and record a focus question and design an experiment to find evidence for the predictions and hypothesis they make. (What will happen if the factor is changed? Explain why.)
- Focus Question.
- How does the volume of the water effect the rate of flow?
- Increasing the volume will increase the rate of flow.
- Water has weight and exerts pressure. The more water in the container means more pressure. The higher the pressure the faster the rate.
- Using the same container put different volumes of water in it and record the amount of water that drains outs in 30 seconds. To maintain a constant rate of flow water will be added to keep water at a constant volume. Record 3 trial at 4 different volumes and calculate rate.
- Make a table of time, volume, volume added, height, type of container.
- Reflect on your prediction and hypothesis. Did your results match what you said would happen? What explanation or new experiment might you try next to help solve the problem of what factors control the rate of flow?
Collect data and analyze results.
The lab should have all the needed equipment.....water, plastic containers, nail and a heat source to make new holes, clock, beakers or graduates to measure volumes, and the most important device.....MOP AND BUCKET, also SPONGES.....
Students should be working in pairs or threes and should have an experimental design to follow. Check them off and let those most prepared start first. Move around the room and check their quality control and question them about what is happening and get them to try to explain the results they are getting. When the data is collected each group should discuss their findings and be prepared to report.
Present preliminary findings and find any points of controversy or descrepancy
Using sheets of paper large enough to see from a distance (20inx20in.), have each group record their focus question, prediction, hypothesis, data, and conclusion. Post the report in a visible area. Ask groups to read through 3-5 and record any questions they might have about how the data was collected or the logic or conclusion that was made. Look for any pattern or relationship that seems obvious and write a statement about the effect the factors that were tested had on the flow rate.
Redefine the problem in terms of pressure and force and discuss.
As a true believer in the fact that Science NEVER Sucks, I would appreciate any input from you concerning the topic of suction, air pressure, and vacuums. Comments on your experiments and special activities or demonstrations that you may have about this mysterious topic would be welcome. I hope that you try some of these investigations in your own classroom. Just remember to let your students do the work of explaining and theorizing. The things they come up with will surprise you and your students will enjoy taking ownership of their learning while confronting the perceptions they have of the mysterious world around them.
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