Since I used the PUM/ALG introduction to energy to define work and derive quantitative energy relationships (described in a previous post), I still had all these cool energy relationships to use as testing experiments for conservation of energy.
Rather than ask everyone to do the same paradigm labs, I gave students free reign to design their own experiment. Some chose experiments based on dropping stuff straight down, or on a ramp. Many chose something related to elastic energy, as shown below, but there was a lot of variability in the details of the experiments.
Each group was asked to predict what they’d have to graph in order to get a linearized graph, and calculate an expected value for the slope based on parameters like mass and spring constant. THEN they collected the data and compared their actual slope to the predicted slope.
This group did a similar launching experiment, but used a push-pull spring scale to launch the cart. They got a slope that was lower then their predicted value, and interpreted it to mean that a significant amount of energy was dissipated within the spring scale when it popped forward.
Since we’ve already defined work, we can use this as another quantifiable relationship. This group looked at the effect of stretching distance on sliding distance. (This is precisely the same experiment done with my ninth graders, but the AP students calculate both a predicted and experimental value for the linearized slope.) They attached some mass to the dry erase marker to increase the sliding friction to a large enough value that they could measure it.
This was a little crazy, and we could have used a little more lead time preparing, since they didn’t have much experience with linearizing, but it ended up being pretty awesome!
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