How Students Learn History, Mathematics, and Science in the Classroom (2005) / Chapter Skim
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11 Guided Inquiry in the Science Classroom
11 Guided Inquiry in the Science Classroom
Pages 475-514
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From page 475... ...
The students had performed reasonably well on questions of the sort that asked, "What would happen to the force if we increased the distance from the planet? " They supposedly understood something about gravitational forces, resistive forces of air resistance and friction, and the idea of force in general.
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From page 476... ...
What good is having my students know the quantitative relation or equa tion for gravitational force if they lack a qualitative understanding of force and the concepts related to the nature of gravity and its effects? They should be able to separate the effects of gravity from the effects of the surrounding air.
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From page 477... ...
The activities involved are designed to motivate and develop a sense of the interrelationships between ideas and events. The expected outcome includes qualitative understanding of ideas, not necessarily formulas.
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From page 478... ...
At the beginning of this unit on the nature of gravity and its effects, the teacher poses the following situation and questions asso ciated with Figure 11-1. - Vacuum inside a bell jar Nature and Effects of Gravity Diagnostic Question Glass dome with air removed Scale reading = 10.0 lbs Scale reading = ______lbs FIGURE 11-1 A diagnostic question to use at the beginning of this unit.
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From page 479... ...
Half of those suggest that the scale reading would go to zero in the vacuous environment. About a third of introductory students believe that the surrounding air has absolutely no effect on the scale reading regardless of the precision of the scale.
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From page 480... ...
Some suggest the scale will go to zero "with no air to hold the object down." Others suggest, "The scale reading will not go to zero but will go down some because gravity is still down and the weight of the air pushes down too, but since air doesn't weigh very much, the down ward air won't be down much and the scale reading won't go down much." Some students suggest that the scale reading will increase (slightly or sub stantially) "because there is no air to hold the object up.
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From page 481... ...
Asking speakers critical questions to clarify what they are saying or to help them give more complete answers and explanations fosters their own engagement and learning. With most of their initial thinking having been expressed, I encourage students to share potentially contradictory arguments in light of the candidate explanations.
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From page 482... ...
I ask, "What can we con clude about the effects of air on the scale reading? " Some students suggest, "Air doesn't do anything." Sometimes to get past this response, I need to prime the discussion of implications of the results by asking, "Do we know air has absolutely no effect?
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From page 483... ...
And apparently gravity is not caused by air pressure pressing things down." Activity A1 Activity A1 is a simple worksheet asking students to review their answers to questions about their initial ideas, other ideas that have come out in discussion, and the results and conclusions from the preceding benchmark lesson. Typically, I hand this summary sheet out as homework and collect it at the beginning of the next class.
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From page 484... ...
Groups of three or four students each are assigned to "major" in one of the elaboration activities and then to get around also to investigating each of the other activities more briefly. In every case, they are asked to keep the original bell jar experiment in mind: "How does this activity help us understand the bell jar situation?
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From page 485... ...
The latter need help making sense of this argument. Most are willing to say tentatively that it makes sense that the air pushes up and are more convinced after they see the various directions in which air pushes in the other activities.
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From page 486... ...
the top hole while water is coming out the lower holes. They con clude that at the top hole, the outside air must push the hypothetical droplet into the water since that is the direction the air goes.
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From page 487... ...
They get engaged in these simple, common activities, and challenged, they need time to come up with and test explanatory ideas. So I now plan for students to have two class periods in which to complete their major activity, briefly visit each of the other activities, and prepare to present their findings to the class.
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From page 488... ...
Note, however, that this is going back to the conclusion that water pushes up, with no mention of any downward push. Many textbooks let students off the hook at this point: "This upward force by the water is called the buoyant force." But this prevents a deeper, more useful understanding involving the resolution of the up and down forces, so I press for more: "Tell me about the pushes by the water on this solid, metal cylinder." Several students jump in with claims based on their previous experiences.
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From page 489... ...
Building an Analogy to Understand the Benchmark Experience Now that it appears the students understand the weighing-in-water situation, I direct them back to the weighing-in-a-vacuum situation. "So, what does all of this tell us about the situation of weighing under the bell jar?
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From page 490... ...
Up to this point, I have been at tempting to identify students' understandings about the pushes of the sur rounding fluid (water or air)
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From page 491... ...
Typical questions related to the key ideas of the preceding activities might juxtapose three situations involving weighing a solid object -- the solid object in air, in water, and in a vacuum -- each object suspended from a string attached to a spring scale. A first question checks on the students' recall of the specific results obtained and asks them to put the expected scale readings in order assuming the scale has the precision needed.
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From page 492... ...
Students should be able to see science as involving many questions as yet unanswered. Although there are still many unanswered questions about gravity, the students do know a great deal about what it does and about the variables on which the strength of the gravity force depends.
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From page 493... ...
Benchmark Lesson: Making a Torsion Bar Do the Twist In the classroom, several meter sticks are hanging from their center points from strings attached to the ceiling. They should be hanging so that each meter stick is horizontal and free to rotate horizontally.
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From page 494... ...
Now the problem: Suppose one end of a magnet is very slowly brought near (but not touching) a sphere on one end of each torsion bar.
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From page 495... ...
. In guided inquiry, the teacher needs to monitor class ideas as they exist initially and as they develop.
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From page 496... ...
I show a piece of film that demonstrates a torsion balance experiment similar to what we have been observing during the first half of the class period. In the film, a meter stick is again used as the torsion bar.
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From page 497... ...
Then the students watch the film as the bar slowly twists such that the bottles get closer to the boxes. Because the effect is so unbelievable to students and because an indirect measure of the movement of the bar is used in the film, I talk the students through the procedure, the results, and the final conclusion: Teacher Do you understand the procedure?
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From page 498... ...
Teacher What would happen to the spot of light if the meter stick twisted? Student 5 The spot would move.
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From page 499... ...
The gravitational effect of a box of sand on a bottle of water is so weak that it requires a very delicate setup. Although Sir Isaac Newton, in 1687, suggested every object in the universe pulled on every other object in the universe, it really wasn't until about a hundred years later that another scientist named Henry Cavendish built a very sensitive torsion balance and was able to see evidence of gravitational attraction happening with ordinary things in a laboratory.
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From page 500... ...
"yiyam." As I beat the pairs of hits faster and faster, the chant begins to sound more and more like "ohwhat afool Iam." The bell rings, and the
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From page 501... ...
of Gravitational Force Depends The purpose of the next series of lessons is to build a case for students to believe that the magnitude (size) of the gravitational force grows as each of the two interacting masses becomes larger, and that the greater the separation distance between the two masses, the smaller is the gravitational force that each exerts on the other.
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From page 502... ...
. Set up properly, the magnet attracts the paper clips and the string pulls on the spring scale, registering a reading even without the magnet touching the paper clips.
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From page 503... ...
Other students suggest we might need more paper clips to lessen the force. Since no one has mentioned the separation distance, I ask how it might make the scale reading lower.
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From page 504... ...
Student 2 See, it's what I thought, less paper clips makes it stronger. Student 3 No it's what I said.
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From page 505... ...
Teacher Good. Now, what do we need to do to test whether the number of paper clips makes a difference in the force?
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From page 506... ...
Anything else? Student 1 See if more paper clips makes the force reading bigger.
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From page 507... ...
Teacher Good. So, we think that strength of magnet, the number of paper clips, and the distance might all change the magnetic force.
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From page 508... ...
From these results we conclude that the magnetic force grows larger with more magnetic "stuff" (paper clips containing iron) , with a stronger magnet, or with closer distance of separation between the big magnet and the iron pieces.
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From page 509... ...
Student 8 Maybe on the mass of the thing, `cuz that would be like the number of paper clips. Student 1 Maybe on the strength of the magnet.
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From page 510... ...
By careful experiments with sensitive apparatus like the Cavendish torsion balance we saw before, scientists have verified that the guesses we just made work out in experiments. That is, the gravity force, evi denced by the spring scale reading, would be smaller if the mass of the earth were smaller, if the mass of the ball being held near the earth were of less mass, or if the ball were placed farther away from the earth.
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From page 511... ...
More mature students can also quantify the acceleration of freely falling bodies and arrive at equations describing the motion in free fall. But younger students can gain a qualitative understanding of free fall as speeding up uniformly, and they can gain some understanding of factors affecting air resistance.
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From page 512... ...
NOTES 1. We use the term "benchmark lesson" to mean a memorable lesson that initiates students' thinking about the key content issues in the next set of activities.
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From page 513... ...
It includes sets of questions for students, reports for teachers, and suggested lessons to address problematic facets of thinking.
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