Paul Caginalp
Task 2
“Why are astronauts weightless?” The question is met with a few comments too low to hear, and some blank stares.
“Because there is no gravity” a couple of students put forth, and I try to make them take back their answers by asking why the moon orbits around the earth if there is no gravity in space.
“Because there is gravity.” Alex comes through for the group, and remembers the answer from a few months ago that Mr. Lake had given them.
“Good. Why does gravity make them weightless?” I probe further, knowing that they haven’t yet gotten to the why of the problem. Another round of blank stares greet me. “who wants to loose weight in here? I have a guaranteed weight loss plan that works in under a second.” A few students raise their hands, bless their bravery. “Ok, stand on your chairs. Now picture yourselves standing on your bathroom scales which are also on the chairs. You are going to lightly duct tape the scales to your feet, then on the count of three, you are going to jump off. Tell me what the scales read when you are in the air.”
“Zero” pipes in Ian, our resident physics expert.
“Why?” I reply with my most common word. No ready reply comes back. There is some discussion between Sal and Ian but both head off the track slightly from the right answer. I let them go back and forth till they come out with something that they both agree on. I only wish the rest of the class paid as close attention to their classmates as I did. Ian and Sal have decided that the scale reads zero because it doesn’t have anything under it to compress the spring against. A close answer, yet just far enough from the truth that they have no idea how brilliant they are being. I tell them they are close, but their explanation leaves something to be desired. I ask the class to figure out how to fix the explanation. No one has come up with anything. I decide to tell them that the scale cannot measure a weight, because it falls at the same speed as you do. Therefore, as soon as you catch up to it, it moves on…you can’t exert any pressure on it. They accept the answer as they accept anything I tell them. “Now why are astronauts weightless?”
“Because the space station keeps falling out from under their feet.” Alex pipes in again.
“Exactly, the space station falls at the same speed they do. So does this explain why they are weightless when they have gravity?” Various nods and yeses come back. Time to move on to the second part of the lesson. “So why are they able to stay up there for months if they are constantly falling?”
“They are so far up there that they have the time to fall.” A couple of the students respond with the answer I was expecting.
“Ok, how long does it take for them to fall to earth from space?” No one knows the answer to this I am fairly sure but Courtney takes a stab at it with a time of 2 months. I tell her that it is way too high. She moves her estimate down by leaps and finally arrives at the time of 22 seconds. “so why can astronauts stay in space if they would fall back to earth in 22 seconds?” I have to give more information it seems, so I decide to ask the students to describe the motion of the space station (something they have been doing for a week or more now). I get a few answers out of the blue, but eventually get the answer of accelerating, which is what I am looking for. “Is that it I ask?”
“No. It also has constant velocity to the side.” Jeff has figured out where I am going with all of this. He sees that I am setting them up for another projectile motion diagram, like I have the last two days.
“Exactly. So as they move toward the earth, they are also moving sideways. What kind of motion do they have?”
“Projectile motion” answer a few students.
“A parabola” answers Jake who, like Jeff, has seen where this is going.
This story shows the main form of assessment in my 8th grade classroom. It has been a big switch from the 11th grade where I could assume that they would ask questions if they don’t understand. Some of them will, but most of them are content to remain blissfully ignorant at this stage of their lives. So far, I have found it most useful to keep hammering the same material until they are all completely bored with it. When the class can not pay attention for a minute or two, and then answer questions I know they have the material well under control. The lesson above was the third day of projectile motion. I tried to draw out the common misconception first, which is that there is no gravity in space. After I had that out of the way, Alex provided me with the right answer. Unfortunately, he had no idea why it was right. To explain why, I bring it back to prior knowledge. I bring the discussion to scales. All of them have stood on a scale before, and they know in a general way how they work. Ian was able to take it to the next step and realize that a scale with nothing pressing on the other side would produce weightlessness. I then ask them to apply that to the outer space situation with some success. As soon as one of them makes the leap, the rest can see the analogy that their classmate has drawn. Once we have moved into the projectile motion part of the day it is laced with recall from the previous two days, though Jeff and Jake have jumped far beyond that and are able to realize from the fact that the object is accelerating, and that there is something else going on, that the spaceship exhibits projectile motion which is in the shape of a parabola. I suspect that some people were still just recalling the information as it became relevant, since I heard some shuffling of notes when I asked specific questions, but if they can recall the information on projectile motion from two days ago I am happy. This is most of the assessment that Bill does with his class, and it has been a real struggle for me to read the students well enough. My own unit has homeworks almost every night so that I can see how well they are doing with the material, and I have a few other goals hidden in among the homeworks too, but I feel like I am almost cheating after having to evaluate the students understanding like this for the last few weeks. Bill occasionally throws in a quiz, or a lab to see how they are staying with the material, but mostly he just quizzes them in class. When Bill is doing a unit that involves math he will often do more traditional assessment practices, but once he is out of a math involved unit he reverts back to his ways.
Some example questions from my homeworks involve the students applying classwork to strange scenarios. One question on my homework on Newton’s laws asks why people can move without an outside force being applied to us. For me, the answer of we can’t seems evident enough, but I want to see what the students come up with. It is a hard question for them I think. They have to realize that we get our energy from food, which is one of the outside forces for us. I know I will get other answers along the lines of we use friction between us and the ground to move, or we move down hill faster than up hill because there are outside forces acting on us, and those are fine as long as they can defend them. Another question, this one from one of my quizzes dealing with Newton’s third law, asks how you could get a boat to shore using only a heavy anchor if the boat is at rest in the middle of the lake. There students have to take the action reaction idea, and realize that they can start themselves in motion by throwing a large object. I don’t expect it to cause as many problems as the one above, but if one of the students hasn’t had to apply the third law yet by some freak chance, I expect them to look at this problem and have the light turn on as to what it really means. I want the question to be more of a “wow, I get this now” than an assessment, but it works well for seeing who has gotten to that point also. I don’t think that the students can do very well on the assignments without understanding the material. There are definitely some questions that are made easier, and some that are just using a formula, but I think around 40-50% of the questions are asking the students to apply what they have learned. Furthermore, the demonstration quick writes ask them to analyze what they are seeing and compose an explanation of the phenomenon.
As for assessment informing instruction, the informal assessment informs our instruction every day. We go slower over parts that they are having problems with, or we speed up over areas that they seem to know. Some of our classes are a day or more ahead of the others, though they all got caught up in the last few days before break. If they all bomb a question on a test the 8th grade curriculum allows us to stop and go back over it, and we have enough flexibility that we can slow down and speed up based on the class. Since Bill doesn’t give homework I tended to catch misunderstandings a bit slower than he did, but I have learned to read kids a good deal better because of it.