Day 63: Wrapping Up Friction Investigations



Today students presented a claim and their data supporting it for whether speed, surface area, weight/mass, or surface type affected friction. The results for the two classes are shown below (as multiple groups did each one). I forgot to take a pic of first hour, but they had a dissenter in SA thinking it did not affect friction.  The far right list of Yes and No is the ‘right’ answer.





I was disappointed with the results, but I learned a valuable lesson; good data can’t be rushed. I am under the gun at this point to finish up unbalanced forces by winter break, so we did this experiment very quickly, with no time for revision and with very little actual data. It is very difficult to get good data for this, particularly the speed experiment. When I did the demo lab after we had compiled their data, I put a motion detector up as well as the force detector, so students could see whether I was pulling at a constant velocity (which you have to in order for the force probe reading to equal the force of friction). I legitimately tried to pull with a constant velocity on the medium speed trial, and it wasn’t even close. I’m confident that they found that speed increased friction only because they were actually accelerating the object. I think the surface area experiment is simply prone to lots of random uncertainty. I have seen it done well when I let them talk almost a week to complete it, but I don’t have that time anymore. Which is kind of sad.



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