## Thursday, December 4, 2014

### Independent Friction Labs

At the end of the first term, I give my honors physics students a couple of days to design, implement, and present an independent investigation involving friction. That's about all that I specify, other than the size of the poster and a few details about requiring equations set with software, citations, etc.

This year's crop was great!

This group investigated the "friction" effects of oobleck on a block, dragged through it at constant speed. They determined that the relationship could be modeled in a friction-like way, but only if the "coefficient" was a function of speed.

This group tested the idea that the mass shouldn't affect the acceleration due to friction; three kids wore the same clothes and slid across the floor, using video analysis to determine the acceleration.

This group tested and modeled the friction between interleaved pages of books. They first modeled the friction on a single page, under some number of pages above, and then did a summation to predict the total possible static friction force between the books.

This group tested the classic physics approximation of ice being frictionless. They made pucks out of ice and dry ice, and determined friction coefficients for each.

This group tried to find the optimum pulling angle for breaking the static friction on an object, both experimentally and theoretically.

This group determined the coefficient of static friction between two blocks, then predicted the hanging mass necessary in a half Atwood machine to cause the top block to slip against the bottom block (which is attached to the cart in the half Atwood).

Another half Atwood exploration - they set up a vertical surface on a cart and increased the hanging mass until an eraser would accelerate along with the cart, instead of slipping down.

This group dragged a boat through water at different speeds, trying to determine whether they could model fluid drag as a friction force. They showed that the "coefficient" would be velocity-dependent, so that drag is not really a friction force.

#### 4 comments:

1. Wow! What kind of prompt did you give them that led to such creative experiments?

2. I told them to come up with a situation that they could model or about which they could make and test a prediction; the situation must include friction. That was about it. I did give them guidelines about the posters: http://www.wikiphys.org/index.php?title=IFL_Presentation and gave each group some feedback about formatting and such after they presented to the class; they then revised their posters. I like the presentation on the projector, followed by revision, followed by printing and displaying them in the school. This was the first time that I've done that order, and I'm pleased with the results.

3. Thanks for this post, it was very inspiring. You are clearly doing some very cool stuff in your classes!

Mark Skinner - Physics teacher

4. Thanks! Lots of credit to the kids for ideas, though. It was initially hard to give up some of the friction labs that I had lovingly crafted over the years, but this is much more productive and engaging for students.