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Diagramming Standing Waves

February 14, 2018

Intro to Sound Waves (Brain Dump)

February 7, 2018

Still needs some work, but this combination is seeming like a good intro to sound waves:

(Note: Students have been learning about springs, oscillations, transverse waves on strings, etc)

Discussion: Is air springy?

Students were asked to come up with a list of ways that we interact with air in our lives or make use of air in technology. Students are then asked to consider the question: “is air springy?” If not, why not? If so, how so? (We’ve talked a lot about things that act springy but aren’t springs). Then, what is it about air that can makes it seem so unspringy? When does the springiness of air become more apparent? What properties of air give it this springy quality?

Pressure Gauge Exploration : Students then explore the springiness of air using a vernier gas pressure gauge and a syringe. Students are asked questions about “Equilibrium” pressure, what happens when you compress air / expand air. Why? How does that amount of pressure change relate to amount you stretch or compress the pocket of air in the syringe? What happens when “let go”? How is a pocket of air similar / different than a spring? Students are then guided to make pressure oscillation graphs by pushing and pulling the syringe in out with high frequency, low frequency, high amplitude and low amplitude.

Visualizing compression waves on speakers, slinkies, and a video.

A few demos are done around visualizing– including watching a speaker move in and out, using longitudes waves on slinkies to help visualize what happens when a compressed pocket is not trapped / confined. Using slinkies to model showing compressions pulses, rarefaction pulses, and then sinusoidal longitudes waves as a model for a speaker going in and out at a certain pace.

Then watch this short video, that gives us another visualization.

Playing with Microphones:

Students are then introduced to vernier microphone as a pressure (force) sensor that has the advantage of being able to collect data very rapidly. Students are asked to explore using their voice to create different sounds and see what types of pressure oscillations take place at the microphone. Students are asked to try to make a sound that makes a oscillation at the microphone that is as sinusoidal as possible and to determine the frequency and period.

Students are introduced to range of human hearing, and we why don’t “hear” the low frequency pressure oscillations in the syringe.

Designing an Experiment to measure speed of sound.

Students are then introduced to following notion:. That Sound can be hard to investigate for two reasons… high frequencies and high wave speed (the video claims > 700 mph). The microphone is a technology that helps us get access what’s happening on a short time scale (to measure those high frequencies), but that it can also be used as a tool for measuring the speed of sound.

Students are introduced to Triggering in Logger Pro, and how to make a good pulse by snapping their fingers. Students are showed how to set up a PVC pipe to record sound pulses and their echoes. Studens are asked to design an experiment to estimate the speed of sound from the echo timing data.

Refining our Technique:

Because students are not careful about identifying pulse timing carefully and only typically use 2 data points, we get decent errors and spread in our data. Also some groups will not use correct distance. This gives us an opportunity to clarify the experimental situation and to refine our data experimental technique.

1. Careful data marking–how to identify a consistent feature of pulse, including how pulse inverts upon reflection.

2. Plotting distance vs time of many echoes to use slope.

Using this technique we get really good data for speed of sound. There then are a bunch of lab questions to press students to make connections, including,

– what would and wouldn’t change with a longer PVC pipe.

– what would and wouldn’t change on a warmer day (from text reading)

– to calculate the wavelength for sounds Ross human hearing range based on their speed is sound.

Blah blah blah…

Brain Dump on Wave Speed on Guitar strings Problem Redesign

February 4, 2018

For next time around, here’s the problem I’m redesigning for students to work on during no our first day of traveling waves, which comes after various explorations, discussions, exercises, clicker questions. For context, the day only focuses on making different shapes pulses, measuring wave speed on slinkies, and what factors do and don’t effect wave speed. A lot of this will then orient us to following question. How fast do pulses travel along guitar strings when you pluck it?

Each group will be given a loose guitar string sample and the manufacturers recommended tensions. A guitar will be at front of room for examining and measuring, as is a scale and meter sticks.

The subgoal will

Need to be determining the linear mass density of their string, its wavespeed, the echo time on their string of the guitar (pulse to travel down and back once), and finally how many echoes reach the bridge of the guitar in a second (echo frequency).

Students will add their data and calculations to a large table at front whiteboard in the room. They will need to double check at least one other group’s work.

Follow ups:

1. There will be questions to structure our talk about patterns in data. What patterns do you notice? Which strings had fastest moving pulses, why? How does echo time compare across strings? Etc.

2. We will listen to each string using microphone in Logger Pro and compare period for microphone oscillation to predicted echo time- a gentle pluck can be used to keep the higher harmonics subdued. The two should be close to the same –> I can conspire for them to be the same if needed.

3. Follow up questions might ask about how the acts of using tuning peg and fretting change the echo time, but in different ways.

Still needs lots of detailing, but I just needed to get the overall idea down.

2nd Semester Physics

January 28, 2018

Second semester physics for us includes topics like waves, optics, electricity and magnetism. With this in mind, I’ve been trying to organize my thinking about how the content is different through a lens that isn’t focused on topics, but rather on the shifts in thinking and skills required.

1. 2nd semester has more and more varied non-linear relationships, including more relationships that have non-monotonic or asymptotic behavior. These include, sinusoidal behavior, exponential behavior, Inverse square laws, and whatever the heck the Thin lens equation is.

2. 2nd semester has more focus on describing how behavior changes over space (potential or fields), whereas first semester has more focus on behavior changing in time. Thinking in wavelengths also becomes crucial. We more strongly employ a landscape metaphor for talking about concepts like potential and potential energy. We shift from vectors to vector fields.

3. 2nd semester has more of a focus on properties of media (index of refraction) and space (permittivity of free space) rather than particles (mass) and objects (density, volume, moment of inertia).

4. 2nd semester has a focus on energy flow (transport) across systems, whereas first semester is more focused on energy transformations within a system. This is reflected in need for concepts like wave speed and intensity. Even how we think about power subtly shifts from the rate of energy changes to rates of energy arrivals and departures.

5. 2nd semester has a focus on local conservation laws, whereas first semester relies more on global conservation. This is a result of focusing on flow.

6. 2nd semester has shifts from single variable functions to multi-variable functions. This is most obvious to me with waves. There also just seem to be more interdependent things going on–circuits.

7. 2nd semester has shift from 1D and 2D geometries to 3D, with examples including spherical waves, Coulomb’s law, magnetic fields and flux. The more complex geometries and focus on behavior over space are at heart of interference. Visualization becomes critical.

8. 2nd semester has a shift in scale requiring more fluency with SI prefixes and scientific notation. Nanometers, TerraHertz, fundamental charge values, etc. I’ve tried over the last year to spend time explicitly getting students to start thinking of SI prefixes as adjectives rather than wholly different units, and to become fluent at using adjectives that allow us to talk in whole numbers as much as possible. 180 mJ, 90 nC, 600 microns, 500 THz,

9. There is a proliferation of new units and unit combinations: Watts (J/s), Coulomb, Volts (J/C), Ampere (C/s), Tesla, Weber, V/m = N/c, eV, Ohms (V/A). Last semester I really noticed how much cognitive demand this placed on students and designed more activities to help us build fluency, familiarity, and connectivity.

10. There’s also a ratcheting up of the instrumentation needed to conduct investigations, diffraction gratings, multi-meters, oscilloscopes, etc.

this is incomplete, but I wanted to start getting a record of some of my thinking.

Damped Harmonic Oscillator Energy Graphs

January 28, 2018

So, I got distracted from curriculum development, so here are some graphs I was curious about. They were made on my phone using desmos.

Energy vs Time, including total, kinetic, potential, and thermal.

Energy vs Distance Traveled

Mechanical Energy vs Position

Energy vs Position, including total, kinetic, potential, and thermal.

Now With less Damping

Now Critically Damped (this one is not released from rest)

And of course, no damping

Five Pieces of Unsolicited Advice for (New) (PER) Faculty

January 18, 2018
  1. Be an Advocate for the Field: I have found it important to think of myself as a front-line representative of the entire field of PER, especially research-based teaching and learning of physics. From this perspective, it helps to fill in the gaps of your familiarity with curriculum and instructional strategies that were beyond your range of first contact as a researcher. Maybe you were really familiar with UW Tutorials, or modeling, or ISLE, or SCALE-UP, or PET or learning assistants, or studio physics, or whatever… now you need to be a knowledge resource and even advocate for all of this and more. For me, as a graduate student and postdoc I was more concerned with filling in gaps in my knowledge of research theory and methodology, and it took a fair amount of effort and time to fill in gaps of my knowledge of curriculum. Also as a graduate student, I was trained to be productively critical of physics education research, and to talk in ways that represented that. As an advocate for the entire field, you need to learn to talk as a bit more as an advocate than a critic.
  2. Treat your Non-PER colleagues as experts on teaching–whether its the teaching of their courses, or their students, the departmental curriculum, whatever. Proactively seek out their advice, knowledge, and opinions, even if some or a lot of they say disagrees with your little PER heart. They have a wealth of experience and knowledge to draw from, and some of it will be spot on. A lot of what is spot on will be based on experiences you don’t yet have, or on knowledge specific to your setting and students / curriculum. Try out some of the things they suggest. If it works, let them know. If it doesn’t, say, “Hey I tried that thing you suggested, but it didn’t work. Can you tell me more about how you make it work?” Treating them like a trusted, knowledge colleague on teaching makes it much more likely that they will reciprocate.
  3. Make Amends when you Act out as a Jerk about Teaching: At some point, likely more than once, you will be a jerk about something education related. When you recognize it, let people know you are sorry and make amends. This can happen in all kinds of ways, and it’s important to recognize when you have trampled on someone for the wrong reasons.
  4. Talk about Students and their Learning not Your Teaching: Try not to talk about your own teaching that much, especially at first. Stick to asking your colleagues about their teaching. When you do want to share something about you teaching, do it by sharing what your students are doing. Make it about the students, not about you. Like, “Hey I want to show you something my students did.” …  or “Hey, check out this paper my student wrote.” Keep the focus on student learning and your excitement about what students can do. Over time, someone might start to ask how you got students to do that, and you can share a little bit,
  5. Be a Point of Contact for PER Resources: When colleagues finally do come to you for advice on teaching, don’t moralize or pontificate. Instead, be a provider of resources. Be the advocate for the field of PER and point them to resources that you think are closely related to their question, concern, or issue. Let them know that their concerns and questions are important. Share more of your own thinking later if they come back again to talk about, or as follow up.

Domain Name Update

January 17, 2018

Hi Everyone,

This blog can now be accessed at (no need for the extra wordpress part). This also means there should be no ads. The old url should still work, so no need to change anything.