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

[spoonless.livejournal.com]

I missed the "no friction" statement as well. But I answered "moves down" for the first two and "insufficient information" for the third, since no matter what the coefficient of friction is in the first two cases, it will still move down.

[zandperl.livejournal.com]

Well, so long as we assume μ<1 - although we learn that in intro physics, in reality some materials have μ>1, such as rubber, or under special circumstances, such as two smooth sheets of aluminum which are perfectly clean or two smooth sheets of glass with a film of water between them.

[spoonless.livejournal.com]

Oh, you're right! For some reason, I never knew you could have mu > 1... I'm glad I stumbled onto this poll :)

For boxes, it would seem somewhat unrealistic to have a mu that large. But I guess the whole question was not intended to be realistic.