In a comment to the AP post, “hogeb” asks an excellent question about pedagogy:
I’d like to enlist your advise and the advise of any readers who can provide it. I teach physical science to pre-service elementary school teachers. I try to elucidate the somewhat subtle differences between the application of a force and the just getting in the way of, among other things, and I try to point out why this isn’t just semantics but truly important conceptual skills. I’m not sure they hear me, or how well they hear me, they rarely do well on these questions on my tests. If you can try to go back to the very basics to teach an adult with a clean slate mind, how would you approach these topics, and which concepts in physics are most important for them to know?
There’s been a good deal of research on how best to get people to learn the basic principles of physics, and at least among the people I’ve heard from, there seems to be a clear consensus: The biggest obstacles to learning physics are the pre-existing misconceptions of the students, and the best way to teach them is to confront those misconceptions directly.
The best examples I have for the intro mechanics class use electronic sensors connected to the classroom computer system, that I can project up onto the screen in the front of the room. This may mean that these are unworkable for people at institutions without these resources, but there are books out there with some ingenious low-cost alternatives– I’ve gotten some good stuff out of Robert Ehrlich’s Turning the World Inside Out and Why Toast Lands Jelly Side Down, and there are lots of other resources out there. I’ll describe one of the high-tech versions after the cut, because it’s a nice illustration of the basic process.
When dealing with Newton’s Third Law, the classic misconception question is something like a collision between a heavy truck and a light car, with students asked whether the truck exerts a bigger force on the car than the car on the truck, or vice versa. A lot of them will assume that the truck must exert a bigger force because of the mass difference.
I set up a track in the front of the room, with two carts carrying force sensors that can record the forces experienced by each cart during the collision. I demonstrate the basic set-up (without colliding the carts), and then pass out a worksheet that asks students to predict which cart will experience a larger force in a variety of collision scenarios: equal mass carts, a heavy cart hitting a stationary light cart, a light cart hitting a stationary heavy cart, two carts colliding and sticking together. I give them a few minutes to write down their answers, and then we go through the experiments.
When the sensors are properly calibrated (which is a little fiddly sometimes), it works great. Before each collision, I’ll ask students to vote for which cart will experience the bigger force, and on the first collision with unequal masses, there will be a good number who think the heavier cart exerts a bigger force. Every one of the collisions shows equal forces on the two carts, in accordance with Newton’s Laws, and some of the students are always visibly surprised.
Making them write down their predictions seems a little dorky, but is actually an extremely important part of the process. Everybody I’ve heard talk about this stuff says that making students commit to an answer and then be proved wrong is the only way to force them to really confront their misconceptions. If they’re not forced to commit, or even if they’re asked to privately consider the prediction, the results aren’t as impressive. Misconceptions are remarkably resilient– maybe Dave Munger can explain why one of these days…
As I said, there are lower-tech demonstrations you can use to serve the same basic purpose, and you can even do this with conceptual examples only. “Wheatdogg” offers some good ideas in a later comment to the same thread.
The key is really the process of forcing them to commit to an answer, and then demonstrating the correct result. That combination forces them to admit that they have misconceptions about the underlying physics, and start to correct those misconceptions.