Marks Final Notes - Precision Measurements Pts 1 & 2

This lab is similar to the 121/131 version, but has some significant differences.

• The paper drop is likely the same as the other labs. I always tell the TA's to emphasize to the students that dropping pieces of paper is an EXERCISE. The point of the exercise is to establish the t' test as a method for comparing measured values. They are NOT doing an experiment. This is basically an application of what they learned from the at home exercise.
• No figuring out how to build your own pendulum component. For the pendulum part I give them a specific method for making the measurements. I want to ensure that the students all start with a technique that will give them a chance of making the precise measurements that are the point of the lab. The goals of the pendulum part are as follows:
  • The at home exercise, this lab and the next are all about teaching how to make measurements, assess and account for uncertainties, making informed decisions about how to proceed with a measurement and comparing results. Taken together they lay the foundation for curve fitting in the cratering lab.
  • Another goal is illustrating how to identify and investigate a possible source of bias in a measurement technique. To prevent students from choosing an unproductive systematic effect to pursue I instruct them to consider the possible effects of friction in the pivot point and air resistance. Then come up with a method of testing for an effect and then quantifying it. Students are instructed to check in with the TA before proceeding. The basic thought is that both friction and air resistance remove energy from the system, which should affect the amplitude of the oscillation which should affect the period.
  • I instruct the students to do all their measurements today at 20°.
  • TA's are supposed to review each groups plans and progress to ensure that the work they are doing is plausible and that they have not missed any important considerations.
  • The lab part is not very long, but the TAs have to spend a bit of time at the beginning going over the expectations, grading, academic honesty and AI considerations… Experience suggests that the lab takes 2 to 2.5 hours with a contentious TA who mentors the students appropriately. I am happy with this.
  • Note my use of an attestation which students are expected to append to the end of every assignment. The attestation is basically that everything in their report is their own work unless attributed otherwise.

• The focus of Day 2 is to take the experimental method that was established in Day 1 and test it to see how small of an angle are they able to resolve the difference between the small angle model and the complete calculation model.
• I am making use of the small angle approximation and the more complete calculation as a metric for establishing how well one can measure the period of the pendulum. Discovering or confirming that the small angle approximation breaks down is NOT part of the lab, this is a GIVEN. Again, we are using knowledge of the physics here to provide a non-arbitrary metric for assessing their experimental technique.
• For context as to why one would test the accuracy of a pendulum, I give the example that pendulum will be used to measure the difference in the acceleration due to gravity at different locations on the earth. I.e. they are not doing an experiment in the lab, they are learning how to develop an experimental technique and understand its limitations so that they can know how it will perform when used in a later experiment.
• This lab also introduces the idea of residuals and how plotting and looking at them can provide insights to your data. For this I ask the TA's to look for a convenient point to have everyone stop for a group discussion on the subject. Not all groups need to be finished, but everyone should have 3 or 4 data points to work with.