Undergraduate Physics TAs–I love this class

Here is a reflection from one of the undergraduate TAs enrolled in my teaching and learning seminar.

This week I discovered upon reflection that most of the questions I asked were very convergent. So, what I thought had been a fairly good dialogic conversation, was just a disguised univocal one. Last Friday I also noticed that I tended to have a lot of teacher-student-teacher interactions. So as Wednesday approached I tried to remain conscious of this and aim for more divergent questions and group discussions.

One of the biggest things I did differently was that when I noticed a student seemed unsure of themselves about an answer I’d just tell them to try explaining their reasoning to a random member of the group. This usually easily got discussion going and allowed me to avoid the usual teacher-student-teacher interaction. Other than that I got less timid about posing questions to groups and I found questions I initially found barely worth asking provided more discourse than I thought. This helped to remind me that I have to keep in mind that all of this material is entirely new to these students and trivial questions may very well still be worth asking.

A specific interaction I had in which I tried to engage in dialogic discourse using the questioning technique actually resulted because I was not prepared for the question. It was one of the QODEC multiple choice questions that I had looked over, but not really thought about. So, I initially just asked them to explain why they thought the answer they had picked was correct. After that, we were all still a bit unclear as to which answer would be correct, so I suggested we go through each answer and try to see what it would mean if it were correct. Doing this resulted in most of the members of the group talking to one another about why they thought certain answers were good candidates for the correct answer or not. Eventually, in this way we narrowed the answer down to two questions and I got a bit excited and accidentally gave the answer way. I did not realize that I had done so until I asked them why they chose the answer they did and they responded that thats what I picked. Luckily, this did not get them out of having to justify this answer to themselves before they could bring themselves to actually submit it.

Overall, I found that it was actually a bit of a challenge to listen carefully enough to figure out where students are having problems so I could ask appropriate kinds of questions to help lead them to a discovery. I hope to think more about the questions before this next lecture so that I can perhaps have some anticipated question sets prepared.

I love how this student is able to “sop” up ideas from our readings and discussions and use them as lenses on his own experiences in the classroom. I love how honest and reflective he is about what’s happening around him–what he thinks is going well, and what he’d like to improve, what’s it like for him, and what it’s like for students. I love the fact that he writes about being with student in terms of an inclusive “we”–as in “We were all still unclear as to which answer would be correct”. I love that he is managing to keep his mind on sooo much–discussion, questioning, listening to students, soliciting reasoning, etc. I love how at the end he invents the idea of proximal formative assessment, as a challenge he has faced and wants to pursue as a goal.

What is force like?

The student quotes below are in response to the following prompt:

Explain why someone might think that objects can “have” force, or that you can “give” force to an object. Then explain why force is not like something you can have or give. In your own words, what is force like?

I’m curious about which is your favorite and why.

“Because people may be confused with the definition of momentum. They feel that if I give this object this much velocity because it has this much has then I can make it have a huge force when it impacts against something. You can’t give or have force because force is always there, there are different forces acting on everything. Force to me is this like a bully hat is always around and very active but you don’t notice until a bigger force is around to put that force in its place. Sort of… ok I’m not really good at explaining this.”

“Someone might think that objects have force because the objects are the source or cause of the reaction to the force. But, force is just a result from the movement or actions of an object and isn’t anything that an object can ‘have’ or ‘give’.”

“Someone can think that an object has force because when two objects collide they react to each other and this is motion is what people see as force. you cant have force or an item cant have force because force is the energy that is expelled when the items collide with each other. the energy that is expelled on the the second object is force and is only present when the items collide with each other.”

“Someone might think an object would have force because it contains  mass and could therefore put force onto another object. Force is not something you can have or give because it is just the attraction between two objects; it does not contain mass. I would describe force as a push or pull on an object that could cause it to move or accelerate due to some type of attraction between the objects.”

“Someone might think think that you can give force to an object because an object moves when someone pushes on it. You can’t give an item your force. When you put a force on an object it will move.”

“Someone might think that objects have force due to their mass when it pushes an object. Force depends on acceleration and mass, so without acceleration there would be no force even if it had a mass. With a constant velocity, the acceleration will equal 0 and there will be no force.

“One cannot have force because when one object exerts a force onto a second object the second object exerts a force of equal strength and opposite direction onto the first object. Force is like the ability to move objects.

“Someone might think that objects can have force, or that you can give force to an object because you can obviously push or pull something if you wanted to as well a heavy object pushing against you. However, force is not like something you can have or give because force is the direct interaction between two objects when a push or pull is done. You can not have force until it is acted upon an object. Therefore, force is an interaction between objects. The force of an object to another object is equal in opposite directions.”

“You could think that you can give something force because, when you apply force you may transfer it to the object. On the other hand force may just be being applied to the object. Force is what happens when two objects interact.”

“Force is not something you can just have or give away between two objects. It may be common to think it is due to the fact that is what many people have heard throughout their elementary science classes. However force is a relationship between two objects causing motion to occur. The way I think about force is if there is a heavy box on the ground and I am trying to push it I cant simply walk up to the box and touch it and expect it to move. I have to push with my legs against the ground and apply a force through my arms to push the box and cause a movement.”

Objects don’t have a force, a force is exerted on an object. People might think that you can give force to an object because when they push it or pull it them they think that is what would be considered force.”

“An example of someone thinking an object might have force would be pool. When you hit the que ball, you are giving it a force.

“Someone might think that an object “has” force if it doesn’t break when touched. For example, someone might say a chair is applying force when someone sits on it, since it doesn’t break. Someone might also think that by touching or pushing an object this adds force to it. Force is more of a measure to describe how the movement of an object changes – as the result of a change in the object’s mass or acceleration. It doesn’t describe what someone is doing to the object, but what happens as a result of someone’s contact with the object.”

“I think that people get force and momentum mixed up. momentum is determined by the mass and velocity of an object. A car at a low speed crashing into a wall is not going to cause as much force as for instance a 18 wheeler going at a higher speed. I think that’s what people think is force or that fact that you can give something force when really it is momentum. Also, I could apply force by pushing down on a button, but i am applying it not giving the button itself force. Force is an application or influence. It is not transferred, given, or something something already has.

“To me force is something that doesn’t happen until you exert it. If you push something you give it enough momentum to get to where its going, but if it hits something it will exert a force on that object and make that object go while the first object either slows down considerably or stops all together.”

Learning to Value Systematized Ways of Thinking

How should students come to see the value of systematized ways of thinking and approaching problems? I’m not exactly sure, but I’d prefer it look more like this:

As soon as I saw it disappearing from the bottom I thought, “Why didn’t I draw the light rays in my initial sketch?” In fact, I wrote that in my journal, if I would have drawn the light rays, how I have been drawing them, with the “cross action”, I would have made a more accurate prediction. Because I didn’t draw the rays as we discussed in class, I went back to basic thinking–like shining a flashlight on a wall and covering it with my hand. I didn’t really take into account the path the light takes when it passes through a small opening.

Then any of this:


or this

or this

or this

or this

or this

Distinctions: velocity at an instant, average velocity, and acceleration

This week’s online pre-class question:

An object is dropped from a height of 45m and takes 3 seconds to hit the ground. Explain why someone might think the object’s speed just before hitting the ground is 15 m./s. Then explain why that can’t be correct.

Three responses representing very different places students can be:

“First of all, wow! That’s the exact answer I had in mind and that is because if it’s dropped from a height of 45 meters and it takes 3 seconds to hit the ground you would want to divide the 45 meters by the 3 s to speed per second (15 m/s), but that is if it was going at a constant speed. So you also have to keep in mind that it was dropped at rest/zero so the speed will increase slowly not constant. I’m still confused.”

“Someone might think it is that because they would divide distance (45m) by time (3 s) which would come out to be 15 m/s. But that would be the average speed.  To find the final speed you would take the initial speed (0 m/s) and add it to the acceleration (9.8 m/s^2) multiplied by the time (3 seconds). The final speed of the ball before it hits the ground would be 29.4 m/s.”

“Because most people would think just divided 45 into 3 to get 15m/s but we haven’t put in  our minds about the acceleration of gravity, which is 9.8m/s that can round up to 10m/s then if you was to times 10m/s by 3s you would get 30m not 45m.”

Student Projects: Ideas vs Concepts

Here is an introduction from a student project in my physics course, who investigated issues of symmetry in projectile motion:

“Why choose this subject to investigate? Out of all the options to research, why this one? The main and best reason I can give to explain why I chose this is just out necessity… In class, …through visualization [of motion diagrams]we began to realize a possible connection between the upward and downward segments of the path. We started to see the motion as reversing itself after the object reached the top of its path. It was from this, that we as a class began to form that idea that if you throw something up at a specific speed, then when it comes back down and gets to the same height that it must be moving at the same speed.”

And here is another introduction from a different student studying the same phenomena

“The purpose of our experiment was to determine if the speed of a ball being thrown up is equal to the final speed of same ball going down. The motivation for this experiment was in part based on Galileo’s own experiments with gravity. Galileo, an Italian physicist, determined that the force of gravity is constant and objects fall at a constant acceleration toward the earth. He determined this by dropping two cannonballs of different size off of the Tower of Pisa. The law of parabolic fall states, “The distance traveled by a falling body is proportional to the square of the time it takes to fall.”

There are likely many different things to see and ways of responding to these different introductions. But, these two different introductions tell the story about the difference between ideas and concepts. Kevin Pugh, an educational psychologist, writes here about ideas: “Ideas are possibilities that must be acted upon and tried out… Ideas are ways of being in the world… They are inseparable from human experience.” Writing about concepts, he states, “Concepts are established meanings (classics)…When intellectual products attain classic status, they become isolated from the conditions in which they had an original significance and from their potential consequences for everyday experience. As a result, their importance is reflexively accepted, but not fully appreciated…”

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