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I pulled off a really awesome teaching moment in drop-in tutoring today. Towards the end of the time slot, there were only two students still there; one in Physics 7B (which is currently covering vectors, forces, and momentum) and one in Physics 7C (which is currently covering electrical forces).
I spent some time helping the 7B student practice drawing free body diagrams, in which an object is represented by a single point and all forces acting on the object are drawn as vectors emanating from that point. She seemed to be picking it up pretty well, so I left her with a few more practice problems and moved on to the 7C student.
The 7C student had been in drop-in tutoring before to get an explanation of the forces charged objects exert on each other. He was currently being puzzled by a problem about a balloon sticking to a wall due to an electrical charge, and having trouble understanding what force was holding it up. I suggested that he draw a free body diagram on the chalkboard, and right away he filled in the force of gravity pulling the balloon down and the electrical force pulling the balloon into the wall, but couldn't think of any other forces acting on it, meaning the balloon "should" move diagonally downward and into the wall.
"So is the balloon going to move through the wall?" I asked. No, of course not. "Then what force is keeping it from doing that?" He couldn't remember. "Do you remember doing free body diagrams in Physics 7B?" He smiled sheepishly and shook his head. At that point I realized that the only difference between this and a typical 7B problem was that one of the forces is electrical, and that was already on the diagram anyway.
Aha, I thought, I have another untapped teaching resource right here in this room!
"Hey, 7B student!" I said. "You're doing free body diagrams right now; what's keeping this balloon from pushing through the wall?"
"The normal force from the wall on the balloon!" she replied cheerfully.
"Exactly! And if there's a normal force mashing the balloon and the wall together, what other force is holding the balloon up?"
They chewed on that one for a while, and finally both got "Oh! Friction!" when I re-drew the diagram sideways (they're not accustomed to thinking of friction on a vertical surface). After that everything fell into place and the rest, as usual, was just algebra.
Thus having saved the day, I donned my hat and cloak and flew home.
Anyway I thought it was really neat that I was able to simultaneously bring together students from two different classes to solve one problem, give the 7C student a review of 7B material, give the 7B student a preview of 7C material, and let them both feel like they had accomplished something. I love my job.
I spent some time helping the 7B student practice drawing free body diagrams, in which an object is represented by a single point and all forces acting on the object are drawn as vectors emanating from that point. She seemed to be picking it up pretty well, so I left her with a few more practice problems and moved on to the 7C student.
The 7C student had been in drop-in tutoring before to get an explanation of the forces charged objects exert on each other. He was currently being puzzled by a problem about a balloon sticking to a wall due to an electrical charge, and having trouble understanding what force was holding it up. I suggested that he draw a free body diagram on the chalkboard, and right away he filled in the force of gravity pulling the balloon down and the electrical force pulling the balloon into the wall, but couldn't think of any other forces acting on it, meaning the balloon "should" move diagonally downward and into the wall.
"So is the balloon going to move through the wall?" I asked. No, of course not. "Then what force is keeping it from doing that?" He couldn't remember. "Do you remember doing free body diagrams in Physics 7B?" He smiled sheepishly and shook his head. At that point I realized that the only difference between this and a typical 7B problem was that one of the forces is electrical, and that was already on the diagram anyway.
Aha, I thought, I have another untapped teaching resource right here in this room!
"Hey, 7B student!" I said. "You're doing free body diagrams right now; what's keeping this balloon from pushing through the wall?"
"The normal force from the wall on the balloon!" she replied cheerfully.
"Exactly! And if there's a normal force mashing the balloon and the wall together, what other force is holding the balloon up?"
They chewed on that one for a while, and finally both got "Oh! Friction!" when I re-drew the diagram sideways (they're not accustomed to thinking of friction on a vertical surface). After that everything fell into place and the rest, as usual, was just algebra.
Thus having saved the day, I donned my hat and cloak and flew home.
Anyway I thought it was really neat that I was able to simultaneously bring together students from two different classes to solve one problem, give the 7C student a review of 7B material, give the 7B student a preview of 7C material, and let them both feel like they had accomplished something. I love my job.
