Overall I am not thrilled with this lab. I think the final lab of the quarter on moments of inertia could be expanded into a two part lab, with part 1 taking the place of this one.
As it stands:
This lab revolves around using the wheel sensors on the iOLab to measure acceleration.
The intent is for students to go through the process of figuring out a way to determine how well the device measures acceleration, test for biases and then correct the bias and retest. So it is about the process of developing a part of an experiment where you need to know how well your apparatus performe.
The basic flow of the lab is as follows:
Come up with a way of testing the accuracy of the device under controlled conditions where you can predict what the result should be. The most straight forward way to do this to setup an experiment where you roll the device down an inclined plane. It is easy to use newtons laws to predict what the acceleration should be. There are surely other ways to do this, but I instruct the TA's to “guide” the students towards this idea if they are not converging on a reasonable method. Big downside here is that the students are expected to “guess what I am thinking”. I spend a lot of time during training talking with the TAs about how to “guide” the students down the path to a productive solution.
Students are expected to work out the theory for predicting the acceleration. I was wanting to give the students an opportunity to use their knowledge of physics to figure out how to do something.
After a group comes up with a plan and a prediction, and the TA has signed off on it, then they do the measurement. They are expected to establish repeatability as well as properly assess uncertainties in measured quantities. In principle I like this part of the lab because the uncertainties in the measurements are easy to identify and assess. The expectation is that energy loss from the wheels and unevenness of the surface are large enough that the students can show a statistically significant difference between what they measure and what they predicted. In practice I do not believe that students find it nearly as interesting to pin down uncertainties as I do and they really just do a sloppy job with this part.
The students should certainly measure a smaller acceleration than predicted, and for the obvious reason that there is energy lost to the wheels. Now they need to figure out how to modify their theoretical prediction, and then test their “corrected” model. To first order adding a frictional force to the problem should move things in the correct direction.
Once they have a new model they need to do a new experiment to test it. For example they can figure out the energy lost due to friction by giving the iOLab a push UP the incline plane and letting it roll back down. The deceleration on the upward motion is not the same as the acceleration on the downward motion. The difference being the effect of friction.
The final part of the process is to take their corrected model, with the experimentally determined frictional factor, and test it in a way that is independent of how they assessed the friction. Meaning not using an incline plane. Simplest way of doing this is to give the device a shove in the horizontal plane and predict how far it will go before friction brings it to a halt.
One of the things I liked about this lab was that everything involves straight forward kinematics, and conservation of energy. This makes it easy to build models. Also, the wheel sensors in the iOLab device provide displacement, velocity and acceleration data which students have to figure out how to use to get what they need.
I think the pitfall of this lab is obvious. The old game of telling students to figure out what I have already figured out works well, and relying on TA's to guide them to the correct solutions. The experimental parts all work well, and you can go down quite the rabbit hole tracking down energy losses and seeing how accurate you can make the measurement… but we all know how successful it is when we encourage students to have fun exploring the rabbit hole.
I strongly recommend replacing this lab.