Unit 2.1: Why are waves created and what is the point of them?

Sandra Penny, Russell Sage College

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Initial Publication Date: September 5, 2024

Summary

Waves are observable all over the place, so why do they exist? Students analyze properties such as wave speed, distance traveled, and time elapsed through their own explorations. They are introduced to new lab concepts (accuracy and precision) and new quantitative skills (interpreting graph data and proportionality). Students are also introduced to the Hunga Tonga volcanic eruption, which sent a shock wave that encircled the globe about three times. This eruption will serve as a motivating question throughout the unit.

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Learning Objectives

After completing this unit, students will:

  • Identify and distinguish between accurate and precise measurements in order to articulate how error affects a measurement.
  • Develop a model of waves to describe patterns in terms of amplitude, wavelength, wave speed, and period.
  • Use mathematical representations to support a claim regarding relationships among the time elapsed/period, distance traveled/wavelength, and speed of a traveling wave pulse.
  • Develop the concepts of direct and inverse proportionality in order to determine the properties of the wave that have direct and inverse relationships.

Context for Use

This unit provides an interactive introduction to making observations about waves, wave propagation, and wave properties, and it is a crucial building block toward our ultimate goal of understanding the Hunga Tonga volcanic eruption. This material is suitable for any undergraduate level and no prior knowledge is assumed except for the very basic introduction they have seen in Unit 1 on units and unit conversions.

Students will utilize quantitative skills: interpreting direct/inverse proportionality; calculating and interpreting mean and standard deviation; inserting a best fit line to data and interpreting the results as physically meaningful from governing equations; using simple equations to make predictions and draw conclusions about data; and performing unit conversions.

The materials in this unit will take 170-200 of class time. The lab for this unit is done in small groups and works best in a smaller class or a lab meet-up.

Description and Teaching Materials

Teaching Materials:

Pre-Class reading materials and assignment:

Introductory Lab: Properties of a wave on a slinky

  • Unit 2.1 Slides Unit 2.1 All Slides v2 (PowerPoint 2007 (.pptx) 6.5MB Aug30 24)
  • Materials needed for each group of 3-4: one slinky, two meter sticks, one time measuring device. Table clamps and/or rods to anchor one end of the slinky in place can be helpful. Stopwatches can be provided, but students will probably prefer to use their cell phones (cell phones have both a more precise timer and can record video).
  • Lab: Properties of a Wave on a Slinky Instructor notes -
  • Activity: Accuracy, and precision with Usain Bolt peer data collection file Unit 2.1 Usain Bolt Measurements v2 (Excel 2007 (.xlsx) 9kB Aug30 24)
  • Unit 2.1 Growth Mindset Dispersion Challenge Question handout Unit 2.1 Growth Mindset Challenge Question v2 (Microsoft Word 2007 (.docx) 668kB Aug30 24)
  • Unit 2.1 Reflection Assignment and Rubric U2.1 Reflection Assignment and Rubric.docx (Microsoft Word 2007 (.docx) 263kB Feb5 24)

Scientist Spotlight Full Resource (In this unit: Wanda Diaz-Merced): Scientist Spotlight Slides (PowerPoint 2007 (.pptx) 4.6MB Jul8 24)

Unit 2.1 Reflection Assignment and Rubric: U2.1 Reflection Assignment and Rubric.docx (Microsoft Word 2007 (.docx) 263kB Feb5 24)

Pre-Class Assignment(s):

  • Read "Practices of Science: Precision vs. Accuracy" and "Practices of Science: Scientific Error" and answer the following questions:
    • A dart player can see how accurate his or her dart throws are by comparing the location of the thrown darts to the target, the bulls-eye of the dartboard. a) How is this model different from scientists who are measuring a natural phenomenon (e.g., volcanic eruptions, snowflakes falling from the sky, dogs jumping off a dock into the water are all examples of natural phenomenon)? b) Is there a way for scientists to determine how accurate their measurements are? Explain your answer. How might the situation be different if a scientist is trying to measure a natural phenomenon with accuracy?
    • When estimating how long it takes a person to run a 100m sprint with a stopwatch, what types of errors might you make and what sources might have caused it? Can you do anything to reduce the amount of error that might occur?
  • Read two articles about the Hunga Tonga Volcanic eruption:
  • Review the Scientist Spotlight: Read about Wanda Diaz-Merced and be prepared to share something interesting or surprising about her.

In Class, (170-200 min):

Introduction (30 min):

  • In this introduction and overview, students are introduced to this unit's motivating question: "What was that sound?! How can we experience a volcanic eruption from across the globe?" Students are shown videos and visualizations about the Hunga Tonga volcanic eruption and introduced to three waves that it created: tsunami waves, shock waves, and gravity waves. We don't seek to answer the motivating question yet, but students are introduced to some of the important concepts as motivation for the next few weeks of structured activities/investigations/labs. Scientist Spotlight and a recap of the Measuring Sticks lab are also discussed.
    • How can I make this discussion relevant to my students? A faraway eruption years ago might initially seem abstract to some students. In these slides, there are several examples that demonstrate this impressively energetic eruption in a way that connects to your students. For example: A series of photos show what it would look like from space if the Honga Tonga volcano erupted somewhere else (LA and NJ), a video records shock waves that shake the house 73km/45 miles away (instructors should make sure to point out something that is 45 miles away from where students are sitting in the classroom), and there is a dramatic video compilation of the eruption for people who lived nearby.
    • How does this activity provide opportunities for my students to reflect on and communicate their learning? A series of think-pair-share questions about air pressure first prompt students about science and then ask them to evaluate why/whether think-pair-share was an effective teaching strategy. This sequence connects to previous learning in Unit 1 (cross-cutting concepts in Unit 1.3, fast/slow thinking or Gun/Drew brain in Unit 1.1) and also to future learning about air pressure in Unit 3. As a science instructor, you want your students to learn science, but you also want your students to be aware of how effective teaching/learning strategies can contribute to their learning. Metacognition exercises like this (awareness and understanding of one's own thought processes) are powerful learning tools that give your students skills beyond just the science they are learning in your class today.

Class Activity: Accuracy, and precision with Usain Bolt (20 min):

  • In this short activity, students use stopwatches to time a recording of Usain Bolt's world-recorded 100m dash and then use a provided spreadsheet to calculate the mean and standard deviation of all the measurements in the class. This serves as our jumping off point in lab for understanding measurement limits and human reaction time, considering the benefit of multiple measurements, discussing accuracy v. precision, and devising a good technique for timing an event in upcoming lab activities.
    • How can I make this discussion relevant to my students? Usain Bolt's remarkable speed was a worldwide event that was celebrated in 2009. At the time of writing (2023), his record still stands, and he is one of the most recognized names in running in history. His run is likely relevant to your students, but if not, you should consider swapping this run out for another. Have there been any recent Olympics with exciting and short races? Do students at your institution participate in running or swimming? Make sure that the race you select is short (<20 seconds) and that there is a known time to compare to so that you can determine whether your class's measurements were accurate.

Lab: Waves on a Slinky (120-150 min):

  • Warm-Up (30 min): students spend time in small groups discussing and executing a plan to analyze a wave on a slinky with the guiding questions:
    1. How can you develop a wave pulse along a slinky that is the same from trial to trial? Describe your procedure.
    2. How can you use a stopwatch and meter stick to measure the speed of a wave pulse propagating along a slinky? Describe your procedure.
    3. How can you change the wavelength, period, and amplitude of the wave pulse? Describe your procedures.
    4. Do any of the procedures that change wavelength, period, and amplitude also seem to change the wave speed? Discuss.
  • Optional Growth Mindset Challenge question is also included: Did the wave shape change at all as it traveled? Why do you think this happened?
    • Students are likely to correctly guess something about energy dissipation due to forces like friction or air resistance. They're not likely to guess that the slinky wave is slightly dispersive. The file Unit 2.1 Dispersion Challenge Question discusses dispersion both in the slinky and in deep water waves, and you should share this with your interested students.
    • This is a good opportunity to remind your students about having a growth mindset and to challenge themselves to think about things that are hard but interesting to them rather than always just doing the easiest option. There's no reason to be bored in this class while students wait for their peers to finish something.
  • Hypothesis and Experimentation (90-120 min): What are the properties of a wave pulse?
    • Students work in small groups to analyze the properties of a single wave-making apparatus. Specifically, the groups will:
      • Build on the warm-up exercise to iterate toward a consistent procedure to create a wave pulse from trial-to-trial.
      • Develop a method to calculate the speed of the wave pulse, taking into account lessons learned from the Usain Bolt activity from earlier in this unit.
      • Determine whether the average wave speed varies when the shape of the wave pulse varies.
      • Organize their procedure and data into a Science Journal that includes two tables and two figures.
    • Like most labs in this course, students are given goals to achieve, but not a specific set of procedures. Small groups are expected to test out and iterate toward a consistent procedure that allows measurement of the speed of the wave pulse on a slinky. After the warm-up exercise, students leave their current groups to form a new group (this is called a jigsaw activity). This jigsaw provides more opportunities for discussion and challenges the students to come up with a solid procedure.
    • After most data has been collected, the class returns to a lecture format for about ten minutes for a group check-in to note how math/graphing and physics can work together for more data analysis. In this lecture, you will show the students that the slope of a line (slope = rise/run) is the same thing as the speed in a distance v. time plot. This is just the first of several times that you'll ask your students to do this sort of analysis in this course and many will find it challenging. It's fine if your students are still struggling with this after today - remind them to have a growth mindset and that they will get more opportunities to challenge themselves to do this in the future.

Teaching Notes and Tips

Lab 2.1 includes the first of several Jigsaw activities in this course. A description of the purpose and benefits of jigsaw activities can be found on the Pedagogy in Action website.

We're only using single wave pulses for these activities - students will need instruction/demonstration because they might be tempted to make standing waves.

This unit includes one of many Scientist Spotlights. The goal of these is to showcase an array of scientists in fields relevant to the topics of the day, some from long ago and others young and active today, together representing a diversity of people who all have a passion for science.


Assessment

A pre-class assignment is graded for completion only, not correctness. Administer using the same format throughout your course (through the LMS, turn in paper copies, guided discussion/participation in class, etc.). Consider setting the due date an hour or so before your class begins to give you time to summarize where your students sit with these concepts (this is a form of Just in Time Teaching).

The Lab(s) is/are assessed as a Science Journal, as always. Science/Lab Journals General Instructions/Rubric (Microsoft Word 2007 (.docx) 2.9MB Aug30 24)

This unit includes a Reflection. These are assigned at the conclusion of most units (typically every 1-1.5 weeks) and ask students to demonstrate higher-order thinking by putting their learning in their own words and also to apply their knowledge in new and novel situations. Reflections should be about 500 words and they should both discuss content that reflects understanding and thoughtfully reflect on the materials.

  • In the Unit 2.1 Reflection, students are asked to read the Visionlearning article "Using Graphs and Visual Data in Science," discuss why graphical representation of data is often a better choice than a table of numbers, and interpret their data from Lab 2.1 using the procedure outlined in the article.

References and Resources

Some references and graphics for the Hunga Tonga eruption. Some but not all of these are in the lecture slides for this unit: