C.1 reading

C.1: Initial Model of Static Electricity © 2023 PEER Physics C.1 N ATURE OF S CIENCE R EADING Instructions: The purpose of this Nature of Science reading is to contextualize and formalize the Crosscutting Concepts and Science Practices from this activity. Physics principles (Disciplinary Core Ideas) were formalized in the Scientist’s Ideas reading. These three pieces– Crosscutting Concepts (CCCs), Science Practices (SEPs), and Disciplinary Core Ideas (DCIs) - are often referred to as “the Three Dimensions” of science learning. As you read, consider the ways you engaged in and with the three dimensions throughout this activity. C.1d CCCs – Evidence-based models are used to make predictions and explanations: The process of developing your initial model of static electricity involved several ideas that span different natural science fields. For instance, all scientists try to find patterns in evidence and use scientific models to make predictions and build explanations about phenomena. Studying static electricity requires identifying patterns in empirical evidence. You have been making observations (data) and using it as evidence to support claims. Evidence collected through experiments is called empirical evidence . Scientists use empirical evidence to look for patterns , which are things that repeat, or always seem to happen in a similar way. In this activity, an example of a pattern in your empirical evidence is that every time you rubbed a balloon with fur, the balloon started being attracted to other objects. Another example of a pattern is that every time two balloons are both rubbed with fur, they start repelling each other. If anyone were to rub balloons with fur using the same materials you did, they would observe similar patterns. Identifying patterns is the first step in making claims and developing explanations about how the world works. Explaining changes in the behavior of objects in an electrostatic system requires ideas about things that cannot be seen directly. After identifying patterns, scientists develop explanations for why those patterns exist. Scientific explanations involve making a claim, supporting it with some evidence (observations/data), and stating reasoning for how the evidence connects to the claim. Sometimes the natural phenomena we observe are brought about by processes that are difficult (or even impossible!) to observe directly, because they are too small or take too long to happen . For instance, in this activity you explored processes involving very small things called electric charges . You decided that electric charges were a good way to explain what you could see, even though you didn’t observe them directly . In this activity you only observed objects being rubbed; or rubbed objects repelling and attracting other objects. This group of objects you observed is an example of a system . You didn’t see electric charges moving throughout the system, but your explanation still involved claims about them. For instance, you explained that an object becomes charged when it is rubbed, and you made claims for why the behavior of objects changed because of what rubbing did to their electric charges.

C.1: Initial Model of Static Electricity © 2023 PEER Physics Models can be used to predict the behavior of objects in an electrostatic system. The ideas scientists develop to explain the patterns they observe, as well as the ways they try to mentally visualize what could be happening at scales they cannot see directly, are building blocks for a scientific model for that phenomenon. Your initial model for static electricity already includes claims, ideas, and visual representations that help explain the patterns you identified in your observations. For instance, your model includes ideas about positive and negative electric charges, claims about their behavior, and ways of drawing them. Scientists use models to make predictions about phenomena, but it is normal for initial models to make incorrect predictions. In this activity, you used your model to make predictions. For instance, by combining your ideas about electric charges with your observations of attraction between charged and neutral objects, you made predictions about what might be happening inside neutral objects when charged objects are brought nearby. C.1e SEPs – Building evidence-based models and arguments: One of the most important scientific practices you engaged in was the development, application, and revision of scientific models. To develop your model, you engaged with your classmates’ models and interpretation of evidence, through a process called argumentation. Building scientific explanations and models about static electricity involves combining ideas and evidence from multiple different sources. In this activity, you applied your initial model to make predictions and build explanations for your new observations. Those explanations were based on your investigations, your ideas, and the ideas of your classmates. Notice how your scientific predictions and explanations are almost always based on scientific models , which can be revised and discussed by multiple people. Models help scientists organize and keep track of important scientific ideas and evidence, and they are useful for simplifying and focusing our thinking about complex phenomena. All sciences require that their scientific models for phenomena be constantly tested and revised to be able to explain new evidence, and you did this with your own model for static electricity in this activity. For example: ▪ Your initial evidence suggested that objects become charged through rubbing, and later you used new evidence to make the claim that some objects can also become charged through ripping. ▪ You initially were able to infer that the T and B tapes were always oppositely charged, but upon gathering new evidence, you added details to your model to conclude that the T tape became positively charged and the B tape became negatively charged.

C.1: Initial Model of Static Electricity © 2023 PEER Physics C.1 3D Q UESTIONS Respond to the following questions individually in your lab notebook: 1. After rubbing balloons with fur, a student claims , “The amount of repulsion between two balloons depends on how much I rub them.” Do you have evidence from this laboratory about any other factors that might influence the amount of repulsion? If so, which ones? If not, how could you investigate them? 2. Imagine that one of your group members makes the following statement when trying to figure out the net charge on each tape. What reasoning from this activity would you use to respond to them? Dee 3. After rubbing a balloon with rabbit fur, Amina makes the statement below. Her statement includes a strong assumption that she is not aware of. What question would you ask her to help her strengthen her model-based reasoning? Amina 4. In this activity, you observed that both positively and negatively charged objects attract neutral objects. Did you expect this to happen? Do you feel confident explaining why this happens, and if not, what questions do you still have about this phenomenon? We knew in the first experiment that the balloon becomes charged when it’s rubbed. Now we know that it’ll always become negatively charged when it’s rubbed, so we can use the balloon to figure the charge on anything! I don’t understand how knowing the balloon becomes negatively charged is supposed to help us. If one of the tapes attracts the balloon and the other repels from it, how do we know that the one that attracts isn’t just neutral?

C.1: Initial Model of Static Electricity © 2023 PEER Physics 5. In this activity, you drew what you thought was happening to the charges within a balloon and rabbit fur when they are rubbed together. Revisit your drawing now, after engaging with the Scientists’ Ideas reading. Are there any details in your Handout that you would change? If so, revise it and briefly explain what led you to make your revision. If not, describe how the Scientists’ Ideas reading supports the thinking you already had. 6. Consider the phenomenon of a girl rubbing a balloon on her long hair, and then observing that her hair stands up and each hair repels from the other hairs. After being rubbed, the hair attracts the balloon. a. How do the patterns from this phenomenon compare to the patterns you observed in the laboratory? List 2-3 pieces of evidence from your laboratory investigations that are either consistent or different from the hair-balloon phenomenon. b. What claim can you make about how rubbing objects affects their static electricity? c. In science, evidence is needed to make claims about causes and effects, and to support explanations about phenomena. What evidence supports the claim that you made in the previous question? d. Apply your model for static electricity to explain how the girl rubbing the balloon on her hair not only made her hair attract to the balloon, but also caused each hair to repel from the other hairs. 7. Consider the following statement: Changes in systems may have various causes that may not have equal effects. a. Brainstorm and record three possible situations involving charged objects where changes applied to the system will not have equal effects . b. Construct a written argument for one of the situations you provided and support your claim with data or evidence from your experiments in this activity. 8. The following questions ask you to consider your model for static electricity in terms of how it can simulate systems involving neutral objects and interactions with those objects. a. A student is considering how to use his model to explain the idea of a neutral object. He makes the claim that neutral objects do not have any charges. Write a response to this student by respectfully providing critiques to this argument. In your response you may ask questions, challenge ideas, and make suggestions. b. Before being rubbed with wool, a balloon is neutral. Draw a picture of the charges in a neutral balloon, according to your current model.