Help me understand a misconception....

[asterroc]

An interesting situation came up in my Physics class today, where two of my students surprised me with a question they asked. To try and understand their thinking so I can teach the content better, I'd like to ask that everyone take a look at the below situation and tell me what you think will happen. I don't care if you know any physics or if you're a professional ear-wax taster, I want to know what you think and why.

In the picture below, Box 1 (m₁) is hanging from a string that passes over a pulley. There's no friction in the pulley, and the pulley has no mass, so it can spin freely. The string is then connected to Box 2 (m₂) sitting on a table. For simplicity, let's assume there's no friction on the table - there's some lubrication between the box and the table.



[Poll #1162218]

X-posted a couple places.

Comments

[rosefox]

If it were going to be in motion, it would already be in motion; there would not exist this state where I could examine it while it was still. Therefore, if it's not moving, it won't move. I just assume that there's other information I don't have that would explain why it's not moving.

I can shift my brain around to think about this the way you're thinking about it, but it's not a way of thinking that comes naturally to me at all.

[zandperl.livejournal.com]

If it were going to be in motion, it would already be in motion; there would not exist this state where I could examine it while it was still.

I'm not saying it is still at the instant this picture was drawn - think of it as stop-motion photography. Or if you do want to call it still, say that I just set up the boxes and just this instant let go of them and snapped the photo.

I can shift my brain around to think about this the way you're thinking about it, but it's not a way of thinking that comes naturally to me at all.

Yeah, I know my students have issues with that too. How do you make that shift in your brain, and what can I, as a prof, do to encourage it? By now my brain is just stuck in that mode so I'm not clear how it got there or if it was always that way.

[rosefox]

How do you make that shift in your brain, and what can I, as a prof, do to encourage it?

I don't go for "What's most likely to be right?"; I go for "Which answer that looks wrong is most likely to be the one the teacher thinks is right?". In other words, my way of solving this has very little to do with physics, and much more to do with having taken a great many exams in various subjects.

The big problem with teaching to the test, or teaching with tests, is that it mostly teaches people how to take tests. I don't think that's actually something to encourage, except insofar as it seems to be necessary for academic success these days. I think that rather than asking "How can I get my students to understand situations that are not real-world situations?" or "How can I get my students to anticipate my meaning when I give them instructions that are presented in the way that makes the most sense to me?", you should be asking "How can I create real-world problems for my students?" and "How can I create problems that don't rely on either presenting instructions a certain way or my students getting used to me presenting them my way?".