193LAB01

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Jan 9, 2024

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Lab 1: Force and Motion I Page 1 of 9 Lab 1: Force and motion I Welcome to your first Physics 193 lab. Each lab your group will work together designing experiments to accomplish scientific goals. First, log in to Google Docs using your scarletmail.rutgers.edu email address and have one group member create a new document. Then, get that document shared with all group members and your TA (find their email addresses on Canvas in the Pages section). This document is where you’ll put together a lab report detailing your work. Your group gets to decide what format makes the most sense for the report but here are two important guidelines: • Imagine you have an additional group member that had to miss lab this week. They need to be able to read through your report and understand what you did as well as the reasoning that went into it. Be clear and complete in your writing. Include drawings, data tables, graphs, etc. as necessary. • DO NOT copy/paste the lab document into the Google doc and treat it as something to fill in. The report needs to read as a coherent stand-alone narrative of what your group accomplished. How to get points in lab Labs are scored out of 50 points. Here’s the breakdown: • 5 points: The pre-lab activity • 21 points: Your total score on the 7 scientific reasoning abilities being focused on that lab. Each is scored from 0 to 3. You will learn more about this during the first lab. • 5 points: The “how this fits into scientific investigation” questions throughout the lab. • 5 points: Other critical parts of the lab (varies lab-to-lab determined by your TA). • 5 points: The “why did we do this lab” questions at the end of each lab. • 9 points: Working hard for 3 hours. Feedback and resubmits • Your TA will give feedback and include your grade directly in the lab report by the start of the next lab. Be sure to look over it right away so you can ask your TA for clarification if needed. • You get to resubmit your lab once for regrading. Resubmits are done in the same document. • Resubmits are always due two lab periods after you did the lab originally. Example: Your TA will have lab 1 graded by the start of lab 2. The lab 1 resubmit will be due at the start of lab 3. Continue…

Lab 1: Force and Motion I Page 2 of 9 An agreement Before getting started with each lab you need to enter into an agreement with the members of your group. At the top of the document your group just created each group member needs to add this statement: <your full name> promises to contribute equally to all course activities and to treat everyone in the course with respect. It is your responsibility to hold yourself to this standard, and for it to be clear to your TA and your group members that you are doing so. We expect you to take this seriously. This is not optional. You will not be able to receive a grade for a lab until you make your own personal statement of this agreement at the top of the lab report. Continue…

Lab 1: Force and Motion I Page 3 of 9 Learning goals of this lab: 1. Make careful observations and look for patterns, then devise and test possible explanations. 2. Observe, record, and represent different types of motion. 3. Represent information in multiple ways. I. Pre-lab activity: Investigating an everyday phenomenon a. Watch this video. Describe what you observe using simple language. https://youtu.be/Bsx7utQ3-7Y b. Devise three different explanations for what was observed. How can you find out which explanation is the best? In science we conduct testing experiments. A testing experiment is an experiment where you use the explanation being tested to predict ahead of time what the real-world outcome of the experiment will be. You do not need to personally agree with the explanation, but the prediction of the outcome must be based on it. After you design the experiment and make predictions based on all explanations that you devised, you then conduct the experiment and compare the outcome to the predictions. c. Briefly describe two experiments you could run to test the proposed explanations. d. For each testing experiment, make a prediction for its outcome based on each explanation that you proposed. (Note: The best testing experiments are those that give different predictions for different explanations). e. Another student suggests the following two explanations: 1. The water collecting on the outside of the glass originates from the water within the glass. 2. The water collecting on the outside of the glass originates from the air outside the glass. They then propose the following testing experiment: You take a glass, put it on a scale, pour ice cold water into it and record the scale reading as time passes. What do each of these student’s explanations predict for the outcome of this experiment? f. Watch the experiment https://youtu.be/x6bNApNaeQA and compare the outcome to the predictions. What does this mean for each of the two explanations? This is known as making a judgment about the explanations. Continue…

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Lab 1: Force and Motion I Page 4 of 9 II. Investigation: A balloon is popped Self-assessment : To help you improve your scientific reasoning abilities we will provide you with self-assessment rubrics. A rubric is a scoring system. A self-assessment rubric is used to help you evaluate your work while you are designing and performing your experiments. The complete set of rubrics is available in the Files section on Canvas. Part of your lab grade each week will come from how well you apply the scientific reasoning abilities chosen for that week. Other rubrics will be used in future labs. Here are the rubric elements your TA will be looking at for this experiment: Scientific Ability Missing Inadequate Needs improvement Adequate B9 Is able to devise an explanation for an observed pattern No attempt is made to explain the observed pattern. An explanation is vague, not testable, or contradicts the pattern. An explanation contradicts previous knowledge or the reasoning is flaw. A reasonable explanation is made. C4 Is able to make a reasonable prediction based on a hypothesis No prediction is made. The experiment is not treated as a testing experiment. A prediction is made but it is identical to the hypothesis, OR Prediction is made based on a source unrelated to hypothesis being tested, or is completely inconsistent with hypothesis being tested, OR Prediction is unrelated to the context of the designed experiment. Prediction follows from hypothesis but is flawed because * relevant experimental assumptions are not considered and/or * prediction is incomplete or somewhat inconsistent with hypothesis and/or * prediction is somewhat inconsistent with the experiment. A prediction is made that * follows from hypothesis, * is distinct from the hypothesis, * accurately describes the expected outcome of the designed experiment, * incorporates relevant assumptions if needed. C8 Is able to make a reasonable judgment about the hypothesis No judgment is made about the hypothesis. A judgment is made but is not consistent with the outcome of the experiment. A judgment is made, is consistent with the outcome of the experiment, but assumptions are not taken into account. A judgment is made, consistent with the experimental outcome, and assumptions are taken into account. Watch this video of a balloon being popped: https://youtu.be/aueaDQxdNAY a. What did you observe about the popping of the balloon? b. Using simple words, come up with several explanations for why the sound is so loud. Refer to rubric element B9 for guidance. c. Two students (June and Bobby) proposed the following explanations: June said that the air escaping the balloon made the loud sound and Bobby said that the breaking rubber of the balloon made the loud sound. Did you come up with similar explanations? How can you test them? Describe the experiments that you would like to conduct. June and Bobby came up with the following testing experiments. Predict their outcomes (specifically, whether you will hear the loud sound) using each explanation that they devised separately (what does the air hypothesis predict? What does the rubber hypothesis predict?): Refer to rubric element C4 for guidance. 1. TE1: Fill the balloon with water and pop it with the needle. 2. TE2: Take a plastic bag, inflate it and pop it with the needle. 3. TE3: Take a piece of rubber from the first popped balloon, stretch it and pop it with the needle.

Lab 1: Force and Motion I Page 5 of 9 STOP - CHECKPOINT ! Before moving on to the next part of the lab call your TA over and discuss the predictions with them. Make any necessary revisions to your work. Checkpoints are not optional. You need to check in with your TA/LA even if you think you completely understand what is going on. d. Watch the experiments (TE1: https://youtu.be/-whsRHDZkzw , TE2: https://youtu.be/xYSsBWXNq7c , TE3: https://youtu.be/FXWrrw7EGFY ) and compare the outcomes with the predictions. What are your judgments of June ’s and Bobby ’s explanations for the causes of the loud sound of the popped balloon? Refer to rubric element C8 for guidance. After June and Bobby examined the original popped balloon they realized that they missed a piece of evidence. Shown is the photo of the original popped balloon. They saw that it exploded into a few separate pieces (not one piece with a small hole). Now, they came up with a new explanation: it is not just the air or just the rubber that makes the loud sound, but the rapid expansion of air through the large opening that appears in the balloon due to the elastic rubber. How can they test this new explanation? They propose to take an inflated plastic bag and hit it wit h the palm of Bobby’s hand so that the plastic bag suddenly tears. If their improved explanation is correct, it should produce a much louder sound than the bag that was just poked with the needle. e. Watch the video of the experiment https://youtu.be/9lCHhTbVW48 and compare the outcome to the prediction. With this new evidence, what is your new judgement as to which explanation best explains the loud sound of a popped balloon? Explain your reasoning. Continue…

Lab 1: Force and Motion I Page 6 of 9 III. Observational experiment: Recording and representing motion Here are the rubric elements your TA will be looking at for this experiment: Scientific Ability Missing Inadequate Needs improvement Adequate G4 Is able to record and represent data in a meaningful way Data are either absent or incomprehensible. Some important data are absent or incomprehensible. All important data are present, but recorded in a way that requires some effort to comprehend. All important data are present, organized, and recorded clearly. B7 Is able to identify a pattern in the data No attempt is made to search for a pattern The pattern described is irrelevant or inconsistent with the data The pattern has minor errors or omissions The patterns represents the relevant trend in the data A6 Motion Diagram No motion diagram is constructed. The diagram does not represent the physical process accurately, either spacing of the dots or the directions and length of v arrows or delta v arrows do not match the motion. The diagram matches the process but is missing one key feature: dots that represent position or velocity arrows, or delta v arrows. The diagram contains no errors in dots, v arrows or delta v arrows and it clearly matches the motion of the object. Your goal is to investigate the motion of a bowling ball in several different situations. This is an example of an observational experiment. The goal of an observational experiment is to begin an investigation into a phenomenon of interest by making appropriate measurements and finding patterns in them. MOTION OF A BOWLING BALL Watch the first 17 seconds of this video: https://mediaplayer.pearsoncmg.com/assets/_frames.true/secs-experiment-video-1 Using the controls at the bottom you can pause the video, advance frame-by-frame, and adjust the playback speed. a. Make careful measurements of the motion of the ball. To do this, decide where you will place the origin of your coordinate system. Measure the positions of the bean bags relative to that origin and record the data. Explain in detail the things you had to consider in doing this. There’s more to it than you might think! (You probably made several decisions unconsciously. Learn to be conscious of the decisions you make so you can think carefully about them.) Refer to rubric element G4 for guidance. b. Use the data you took to classify the ball’s motion: constant rate, increasing rate, decreasing rate, something more complicated? Explain how you decided. Refer to rubric element B7 for guidance. c. Repeat the previous steps for the remaining situations in the video. STOP - CHECKPOINT ! Before moving on to the next part of the lab call your TA over and discuss your analysis with them. Make any necessary revisions to your work. DRAWING A MOTION DIAGRAM See the diagram below on how to construct a motion diagram. This particular motion diagram represents an object moving to the left but slowing down.

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Lab 1: Force and Motion I Page 7 of 9 d. Draw a motion diagram for the bowling ball for each of the four situations in the video. Refer to rubric element A6 for guidance. e. How is a motion diagram different from a written description of the bowling ball’s motion? How is it different from the measurements that you made? What are the advantages and disadvantages of each of these three representations? Explain your reasoning. Continue…

Lab 1: Force and Motion I Page 8 of 9 IV. Observational experiment: Forces exerted on an object by other objects See the diagram on how to construct what is called a force diagram . IMPORTANT! At the moment shown in the diagram the rock is still slowing down as it embeds itself further into the sand. This means the rock is not in equilibrium. a. What do you notice about the lengths of the two force arrows? When the rock finishes slowing down the rock will be in equilibrium. How would you change the diagram to indicate that? Here are the rubric elements your TA will be looking at for this experiment: Scientific Ability Missing Inadequate Needs improvement Adequate A5 Force Diagram No force diagram is constructed. Force diagram is constructed but contains major errors: missing or extra forces (not matching with the interacting objects), incorrect directions of arrows or incorrect relative length of force arrows. Force diagram contains no errors in force arrows but lacks a key feature such as labels of forces with two subscripts or forces are not drawn from single point. The diagram contains all appropriate force and each force is labeled so that one can clearly understand what each force represents. Relative lengths of force arrows are correct. The goal of this experiment is to learn to represent forces exerted on an object by other objects in a clear and efficient way. Available equipment: A heavy object (like a laptop), a light object (like a sheet of paper). Pick up the light object and hold it stationary in your hand. Then pick up the heavy object and hold it the same way. Do you feel any difference? Now we will learn to represent this difference using force diagrams. For each situation (light object and heavy object) do the following: b. List all the objects that interact with the object (c alled the “object of interest” since that’s what we are focusing our attention on). To interact with the object of interest, other objects need to be in physical contact with it — however Earth is an exception – it can interact gravitationally from a distance. Explain how you can represent these interactions on a diagram. c. Represent the object of interest with a dot and use an arrow to represent each interaction some other object has with it. Connect the tails of the arrows to the dot. Label each force arrow with an that has two subscripts. The first subscript represents the object that exerts the force on the object of interest; the second subscript represents the object of interest itself. For example, the force that the hand exerts on the object can be written as 𝐹 ⃗ 𝐻 ?? 𝑂 . Pay attention to the lengths of the arrows on each force diagram. Since you are holding the object steady in your hand, should the force diagram be balanced , meaning the upward arrow and downward arrow should have equal length? Refer to rubric element A5 for guidance. d. Explain how a force diagram is a better way than written words of describing the forces being exerted on an object. e. Why are forces represented by arrows and not just by numbers or lines? Continue… F

Lab 1: Force and Motion I Page 9 of 9 V. Why did we do this lab? a. During this lab you performed observational experiments and testing experiments. 1. What is the primary purpose of each of these two kinds of experiments? 2. What features does one have that the other does not? b. What is the purpose of a motion diagram? A force diagram? In what ways are these representations useful?

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