# Week Two (Fa14)

No classes on Monday due to Labor Day.

**Astronomy Lecture**

Students worked through the Motion tutorial over the weekend so we spent Tuesday discussing clicker questions related to the daily motion of stars through the sky and how to relate this motion to the Celestial Sphere. On Thursday we worked through the Seasonal Stars tutorial in class and started the Ecliptic tutorial which students are completing for homework. I also spent a few minutes each day talking about how to use the Rotating Sky simulations from Nebraska.

Students are struggling some with interpreting diagrams and thinking three dimensionally. I’m accustomed to thinking of “into the page” and “out of the page” as potentially relevant directions when looking at a diagram due to physics. I need to remember that thinking about these directions is largely new to these students.

**Astronomy Lab**

This week’s lab focused on scale diagrams and why it is unfeasible to design a scale diagram of the Solar System. I split the lab in two and had one half look up planet sizes and decide on a scale to use such that they could cut out paper circles representing each planet to scale. The other half of the class looked up planet-Sun distances and decided on a scale to use such that they could spread out to scale in the Quad. Groups then shared their results and each group calculated one of their distances using the other group’s scale to see that this results in unreasonably large or small scaled distances. Students also read a short excerpt from Bill Bryson’s Short History of Nearly Everything in which he talks about the scale of the Solar System and discusses the Oort Cloud and how the Solar System extends far far beyond Pluto.

This lab wasn’t really an experiment, but we will be using diagrams all semester that say “Not to scale” so I felt like we needed to talk about what they means. In addition, I wanted to make the scale cut outs and a video of walking the scale spacing for lecture since I didn’t have a good way to do this activity in a lecture room with 30 students.

**Physics 2**

I remember a Colorado paper showing that students explore PhET simulations more thoroughly and do a good job of making relevant observations if you let the students explore freely rather than giving detailed instructions. With this in mind, I’m trying to open up our use of simulations some. I started Wednesday by handing out laptops (1 laptop per 2 students) and gave students 10 minutes to explore the Gas Properties simulation with instructions to see what the controls do and what they find interesting. Walking around, I heard multiple groups notice that if you pump in particles and then increase the gravity the temperature increases. I wrote this observation on the board and said we’d come back to this at the end of class. I then gave students 5 minutes to find as many ways as possible to increase the pressure inside the box. I recorded students’ findings on the board and showed that each finding agrees with the Ideal Gas Law. We then discussed the microscopic origin of gas pressure (particles colliding with container walls) and talked about how this can explain why each change students identified results in an increase in pressure. We finished by talking about the microscopic meaning of temperature and introduced the equipartition theorem but did not have time to explain “degrees of freedom”. At the very end I returned to the gravity-temperature link and discussed this in terms of a sudden addition of gravitational potential energy which is then converted to KE (related to temperature) as the particles fall.

On Friday we talked a little about degrees of freedom focusing for now on translational motion. I walked through an example using the Equipartition theorem to calculate the average velocity of a nitrogen molecule in the air. Our result (~500 m/s) is noticeably higher than the average speed in Gas Properties for the Heavy Species (~425 m/s) so I pointed out that Gas Properties treats the box as 2D and thus there is only 1 kT rather than 1.5 kT contributing to the kinetic energy. I used the simulation to demonstrate that decreasing the volume results in an increase in temperature and (overly?) guided students to view this in terms of work and introduced work done on the gas as the negative integral of pressure with respect to volume. I ended by introducing the 1st law of thermodynamics.

I need to work on timing for these topics. I don’t like introducing a big important idea at the end of class without sufficient time to discuss. I also need to think about what ideas I want us to develop together in class, and what ideas students can be introduced to on their own outside of class either through reading or working through a guided assignment. Wednesday felt very productive but Friday felt like some of that would have been better delivered outside of class. Too much watching me and not enough of students being in the driver’s seat.

**Physics 3**

Last week was largely exploratory with students working together on tutorials and trying to answer various questions in lab so we spent Wednesday summarizing some of our findings and making sure we were all on the same page. This class didn’t feel that exciting but it ensured me that everyone came out of week 1 with the right ideas. Also the first three classes were almost completely devoid of direct instruction so the students might have been in a place to want a little bit of verification (I’m not sure if this is true).

We spent the first hour of Thursday’s lab working on the UW tutorial on Superposition and Reflection. Students saw superposition of wave pulses on Slinkies in the first lab but they didn’t have a formal definition so I lectured for about 5 minutes and then set them to work on the tutorial. Students also recognized coming out of last week’s lab that there were questions on the Mechanical Waves Conceptual Survey about how asymmetric pulses reflect that they did not know how to answer from the previous lab alone. The tutorial went pretty well with students needing some guidance on adding partially overlapping waves graphically but getting the hang of it once I got them started.

The rest of lab period was spent doing a “lab” on how to use the function generator and oscilloscope. I’m a little torn on this lab. The goal is primarily on the basic use of this equipment (there’s a second part to the lab but with the tutorial no one go to it). I think the lab is successful at introducing how to use the equipment, but this is the only time all semester that we will use the oscilloscopes. That being the case, I’m not sure whether it’s worth introducing oscilloscopes in our class. I don’t know how much our introduction helps a student whose next exposure to an oscilloscope is a semester or a year later.

This is the first semester that I gave the mechanical waves survey and it’s the first semester that I’m trying to incorporate some of the UW tutorials, so I’m trying to figure out pacing. I’m going to delay introducing sound waves and move into standing waves on a string next week so that we are prepared for next week’s lab. I’ll introduce sound waves and their representation in terms of pressure deviation vs. average particle displacement the following week along with standing sound waves. I think this will keep us on pace OK but I do feel like there is less breathing room in this unit compared to last semester.