Lab 02 - Virtual Reality Charged Particles

Lab 2 - Virtual Reality Charged Particles Goals • To familiarize students with the NOMR environment and Meta Quest console. • Design and conduct an experiment with well determined independent and dependent variables to test if the simulated charged particles interact according to Coulomb's law. • Estimate random or instrumental uncertainties for measurements. • Create a set of graphs to understand how to linearize a plot. • Make a judgment of the validity of the model being tested based on a well-reasoned argument. • Make qualitative observations of general behavior of the fictitious “Minty particles” that are simulated in the VR. • Synthesize the observations and measurements to develop an empirical model that describes the “minty” particle interactions. Introduction Your goal in this lab today is to quantitatively test whether the interactions between charged particles in a virtual reality (VR) lab obey Coulomb's law. Once that is accomplished (by the halfway point in lab) you will then apply what you have learned to test a new type of particle. Important Note: You should already be comfortable with Coulomb’s Law. You are not looking to education yourself on Coulomb’s Law, you are looking to identify the ways in which this simulation of reality falls short of perfectly reflecting reality. Note: Physics in the virtual lab follows a limited set of models. Most of these models are based on the real world, but none are exactly accurate. It's impossible to perfectly simulate real-world physics, and many rules have been deliberately changed for the next two labs. Explore the Simulation VR headset safety • The headsets should be used only while seated. 5

Chapter 2. Virtual Reality Charged Particles 6 • Students in a headset MUST be given adequate space to move their body and swing their arms. They cannot see their fellow students. Headset users ALWAYS have the right-of-way. • Always ask for consent before touching anyone in a VR headset (e.g. to put their finger on a controller button). • Wipe down the headset (with the wipes provided) between users, every time the headset changes hands. • No one is required to use the headset. If a student experiences nausea or other discomfort while using the headset, they should take it off immediately and notify an instructor. Oculus VR Introduction Guide – Optional If you are new to using the Oculus VR system, an introduction document is available at the end of this lab in section 2.3 on page 18. Launch the Simulation (VR headset operators) 1. Make sure the Oculus headset is connected to the Desktop PC with the braided USB cable. 2. Power on the Oculus headset by pressing and holding the button on the right side of the headset. 3. Be sure to remove the protective lens cover before you put on the headset. 4. You will see a message “Allow access to data”. Select “Allow” using either hand controller. 5. Click “Create Guardian” and follow directions to set ground level. (If prompted to, select “Sta- tionary Boundary” and confirm). 6. From the Apps menu open the NOMR app (it should be at the top left of the screen). 7. Ask your lab partner to open the Quest Mirror shortcut in Z:/VR Labs 8. Press the Play button in Quest Mirror to show on the PC screen what is visible to the VR user. You should now be in the virtual lab, and the screen should be mirrored on the Desktop PC. It is sometimes necessary to re-open the Quest Mirror software on the desktop. If the Quest Mirror software is not functioning, check to be sure the USB cable is connected and repeat from step 3 above. If you have any difficulties, your TA should be able to help you. Familiarize yourself with the VR lab environment by completing the following steps: 1. Enter the code “ 1856 ” into the keypad and press Submit to load today's lab setup. (a) Press buttons by pointing at them and clicking the trigger button on your controller. 2. Create a new positive charge by pointing at the button labeled “Positive” and clicking the trigger. Note: each particle has the same amount of charge, ± q . 3. Point at the newly created charge and hold down the grip button to hold the charge and move it around your space. 4. While holding the charge, push the controller thumbstick away from you to push the charge away. Move the thumbstick toward you to pull the charge toward you. This will work for every movable object in the simulation. 5. Anchor the charge by pointing at it and pressing the trigger. This locks the charge at a point in space and is visually represented by a cage around the charge. To un-anchor the charge, point at it and press the trigger again. • Tip: When you move a particle and then release it, the particle almost always has some initial velocity. To avoid this artifact of your physical manipulation, you can anchor par- ticles as you move them. After you have let go of the particle, remove the anchor, and the particle will now start simulating interaction with the environment from a zero initial velocity state.

Chapter 2. Virtual Reality Charged Particles 8 Checkpoint 1 Discuss with an instructor your understanding of the available measurement tools before proceeding into your experimental design. Designing an Experiment Now, discuss with your group how you will experimentally observe the interactions you are interested in. Brainstorm the potential experimental variables that you could adjust in electric charge interactions in the VR. Make a list of these variables and assign each variable a symbolic representation to use as a shorthand. Indicate whether the variable can be independent, dependent, or controlled. In general, the uncertainties for the measurements of the independent variables and control variables should be much smaller than those for dependent variables. The table below can be used as a template for your list. Variable Symbol Can it be independent? Can it be dependent? Can it be a control? Separation r Yes No Yes Force F Consider the following scientific questions: • How does the force depend on the charge of the particles? • How does the force depend on the separation of the particles? Discuss with your group how you would collect data to answer each of these questions: • Do you expect the force vs. charge graph to have a linear relationship based on Coulomb's law? • Do you expect the force vs. separation graph to have a linear relationship based on Coulomb's law? To learn special data analysis techniques for exploring non-linear relationships, let's test Coulomb's law by designing an experiment to answer the second question. For this experiment, what is the independent variable and the dependent variable? Are there any control variables? Checkpoint 2 Discuss your experimental design with an instructor be- fore proceeding. Data Analysis Graph Linearization In physics, we often investigate how one quantity relates to another by plotting data. If your data graphs as a curve, the quantities have a non-linear mathematical relationship (e.g. y = x 2 ). Non- linear data is more complicated than linear data to analyze. It is hard for the human mind to accurately recognize any specific function other than a straight line. We can take advantage of the human capacity

Chapter 2. Virtual Reality Charged Particles 9 to recognize straight lines by transforming the data such that what we plot on our axes results in a linear relationship. Your goal is to create a linearized plot to see if your data agree with Coulomb's law. Sketch the following plots showing the relationship between the forces, F and the separation, r : • F (on the vertical axis) vs r (on the horizontal axis) • F vs 1 / r • F vs 1 / r 2 • F vs 1 / r 3 Discuss with your group which of the above plots looks most linear and why. Compare Coulomb's law, F = kq 1 q 2 r 2 , to a general formula for a straight line, y = Ax + B . Which quantity in Coulomb's law corresponds to which quantity in the straight-line formula for the plot that looks the most linear? Straight line formula Coulomb's Law y F x A B Checkpoint 3 Discuss these plots and the table above with the instruc- tor before leaving the lab. Plot your data Create a plot for the most linear relationship using a plotting tool like Google Sheets or Excel. You should choose which plotted quantity has the larger uncertainty and include it in the plot. Include a trendline (best-fit) for your linearized plot. Does the best-fit line goes through at least 2/3 of the uncertainty bars? Do the simulated charged particles obey Coulomb's law? Optional Activity: Consider the following questions and how to experimentally answer them • Do the forces between particles obey superposition? • What stable structures can you make with these simulated charges? • If you create a large number of one type of charge, how do they distribute themselves in the room? What can this tell us about the distribution of charges on conductors with sharp edges? Empirical Modelling: The Minty Particle In the first half of the lab, you conducted a model testing experiment; you tested Coulomb's Law. Your goal in this half of the lab is to perform the other kind of experiment, an empirical modeling experiment, to create a model describing the interactions between never-before-seen fictitious particles (dubbed “Minty Particles”) in a virtual reality (VR) lab that do not exist in the real-world. Enter the code “ 5086 ” into the keypad and press Submit to load the Minty Particle lab setup.

Chapter 2. Virtual Reality Charged Particles 11 Develop an Empirical Model Using the data that you gathered from your experiment, your goal is to develop a model for minty particle interactions. Use the table below as a guide to develop your model (the Coulombic model for electric charge interactions is described as an example). Charged Particles (example) Minty Particles Symbolic Representation −→ F = kq 1 q 2 r 2 ˆ r Verbal Representation Define all relevant quantities • The force between two particles with charges q 1 and q 2 is proportional to each charge and has a constant k . • The force falls off with the square of the distance between the charges r . • The force acts in the ˆ r direction, along the line connecting the two charged particles. Note: ˆ r is a unit vector that only indicates the direction. As you develop your model, keep in mind: • You are conducting an empirical modeling experiment. Unlike the model testing experiment that you conducted for Coulomb's law, there is no known model that you are testing. The only “right” answer is the one you make the best case for. • It's normal practice in physics experimentation to revise your experiment and collect additional data as you learn things and make decisions. • An equation symbolizes information but does not necessarily capture everything about the model (such as assumptions that you might be making or limitations of the model). Describe any assumptions you are making and the limits over which you believe the equation is valid. Can you, for example, describe the interactions between two minty particles that are infinitely apart? • One experiment can't fully flesh-out a model. The best model for the minty particle interactions is the one that your group feels best describes them, out of all your group's ideas. You're being assessed based on the quality of your collaborative process - you're not in competition with other groups for the most sophisticated model. • Refer to instructions in the first half of the lab for how to linearize a plot. Checkpoint 6 Show the data you collected to an instructor and discuss your model with them before you leave. BEFORE YOU GO : Be sure to turn off the Oculus headset by holding the power button (on the right side of the headset). Wipe down the headset (with the wipes provided). Verify the headset remains

Chapter 2. Virtual Reality Charged Particles 12 plugged in to the computer after you set it down. Put the eye-protection cover back in place. • Using a plotting tool like Google Sheets or Excel, create a plot of your data with uncertainties, linearized according to the model you proposed for minty particle interactions. • Add a trendline to the linearized plot. • Describe your model for the interactions between minty particles in the VR environment. Ex- press your model mathematically. • Explain each of the qualitative features of minty particles' behavior using your model. Does your model agree with your qualitative observations? • Over what regime does your model apply? Can it be used to predict behavior that you don't currently have the ability to observe? VR Introduction