Unit 2.2: Measuring and Analyzing Waves

After completing this unit, students will:

• Develop a model of waves to describe patterns in terms of amplitude, distance traveled, wave speed, and time elapsed.
• Use mathematical representations to support a claim regarding relationships among the time elapsed/period, distance traveled/wavelength, and speed of a traveling wave pulse.

This unit is a continuation from Unit 2.1 and provides an interactive introduction to making observations about waves, wave propagation, and wave properties. Plan for these materials to take about 70 mins if you only complete the Activity: Use slow-motion video to analyze properties of a slinky wave pulse. Add 90-110 mins if both The Vortex Cannons and Waves in a Bottle extension activities are completed. All of the activities and labs in this unit reinforce concepts from Units 2.1 and 2.2 but do not introduce any new topics.

The materials in this unit were developed for use in an in-person synchronous classroom, and they rely on small group work that is best suited to smaller classes or a lab meet-up outside a traditional lecture room.

Teaching Materials:

Pre-class reading assignments: Waves and Wave Properties or Waves and Wave Motion: Describing Waves.

Unit 2.2 Slides: U2.2 All Slides.pptx (PowerPoint 2007 (.pptx) 6.1MB Feb7 24)

• There is no separate file of instructor notes for the lab activities in this unit, but there are sample student responses and instructor prompts to discussion questions in the notes sections of this slideshow.

Slinky Slow-Motion Wave Speed Slinky Lab Materials

• Materials: computer or smart phone that will open a .mov video file (one for each group). Optional: large-format paper for walls and many markers so students in small groups can write on them. The paper & markers are for a gallery walk to summarize and recap what we've learned about waves.
• Slow motion slinky pulse videos. Instructors could consider having their students make their own video while they are completing the lab in Unit 2.1 instead of using these videos. SloMoSlinkyPulse2.MOV (Quicktime Video 27MB Feb7 24) SloMoSlinkyPulse1.MOV (Quicktime Video 33.1MB Feb7 24) SloMoSlinkyPulse3.MOV (Quicktime Video 33.7MB Feb7 24)
• PhET simulation: Wave on a String

Water Waves in a Bottle (extension lab)

• Materials for each group: a pre-prepared clear bottle or jar (e.g. a mason jar) that is leak-proof containing 1/2 to 2/3 water with blue food dye and the remaining volume containing mineral oil. The jar should be as close to full of fluid as possible to minimize air bubbles. A phone or camera to record video (ideally in slow motion) is strongly recommended.
• Wave in a bottle instructions (for instructor) Wave in a Bottle Lab - Instructor Notes.docx (Microsoft Word 2007 (.docx) 1018kB Jun24 24)

Vortex Cannons (extension lab)

• Materials for each group: Cardboard box with all six sides, box cutters (scissors or utility knife), compass to trace out a circle in the box (optional), duct tape or other seam sealing tape, cell phone to take slow-motion video, meter stick, targets like plastic cups to knock over, and something to visualize the vortex rings (optional but recommended. Try dry ice, a fog machine, or incense).

Unit 2.2 Reflection Assignment and Rubric: U2.2 Reflection.docx (Microsoft Word 2007 (.docx) 70kB Jun24 24)

Pre-Class Assignment(s):

• Read either Waves and Wave Properties or Waves and Wave Motion: Describing Waves (Visionlearning). A diagram of a moving wave is shown. Use this figure to answer the following questions (adapted from the article "Waves and Wave Properties"):
  

  ×

  

  Provenance: https://manoa.hawaii.edu/exploringourfluidearth/physical/waves/wave-and-wave-properties/question-set-waves-and-wave-properties-0 "This document may be freely reproduced and distributed for non-profit educational purposes."
  Reuse: This item is offered under a Creative Commons Attribution-NonCommercial-ShareAlike license http://creativecommons.org/licenses/by-nc-sa/3.0/ You may reuse this item for non-commercial purposes as long as you provide attribution and offer any derivative works under a similar license.
  • 1. What is the amplitude of the wave?
  • 2. What is the wavelength?
  • 3. Can you calculate the period of the wave from this information? If so, what is it? If not, what additional information do you need?
  • 4. Check your understanding of the following terms by defining them in your own words:
    • period
    • wavelength
    • wave speed
• Pay attention to waves noticed in everyday life and come prepared with a list of what you observed.
• If completing the Vortex Cannons Lab: Bring in a cardboard box (bigger is better) to make a vortex cannon. Watch this video starting at 0:50 to see a vortex cannon. Answer the following questions:
  • 1. How does the vortex cannon produce a wave?
  • 2. How can you define the amplitude of the wave coming out of the vortex cannon? How will you try to change the amplitude of the wave pulse?
  • 3. How will you try to change the wave speed of the wave pulse?

In Class Part 1: Slow-motion wave speed slinky lab (70 min):

Introduction (10 min):

• Go through the pre-class assignments: Have students form small groups to discuss their answers, and then go around the room asking each group to answer one or two questions.

Slinky Slow-Motion Wave Speed Slinky Lab (30 min):

• In Groups: Use the slow-motion videos to determine the wave speed of the wave along a slinky. Students recorded these videos in Unit 2.1, or you can use the videos that have been provided.
• Discussion Questions:
  • Discuss how the wave speed calculated based on period and wavelength (today) is related to the wave speed calculated based on time elapsed and distance traveled (last time).
  • Waves transfer energy but not matter. Discuss how your observations thus far in this course are consistent with this statement.
  • Comparing the slinky lab from Unit 2.1 to what you did today:
    • Which of your measurements do you think are accurate? Explain why or why not
    • Which of your measurements do you think are precise? Explain why or why not?

Class-Discussion Recap and Synthesize where we've been (30 min):

• Spend 5 mins using the PhET Simulation: Wave on a String alone, and then in small groups answer the following:
  • What does this simulation tell you that you already knew?
  • What does this simulation tell you that you did not know and found interesting/surprising?
  • Note to instructors: discussing this PhET simulation is part of this unit's reflection assignment. You can choose to skip this in-class introduction for time if need be.
• Considering both the slow-motion slinky activity and the first slinky lab: Some groups may have produced procedures that were more accurate AND more precise - what were they? Why do you think some procedures worked better than others?
• Important properties that the instructor should emphasize in any class-wide discussion: waves transfer energy, not matter; wave speed depends on the property of the medium, not the amplitude or shape of the wave.

Extension Activity/Lab: Water Waves in a Bottle (30 min)

Introduction (5 min)

• Remind the students that we have so far really only explored waves that we cannot see, or that are very challenging to observe. Today we will make direct observations about waves and waveforms in water.
• Start by reviewing the basic parts of a wave (see slides) and how waves are measured. After the review, you can keep displaying the slides of different wave types for the students' reference.

Experiment (20 min)

• Distribute one "wave in a bottle" to pairs or groups of three students to use.
• Instruct them to very carefully and gently create waves with the bottle (by rocking it and rolling it around). Too vigorous shaking will make bubbles! 
• As one student tries generating different forms of breaker waves, another should record with video for capturing stills and reviewing the waveforms. Stills from video capture will be necessary for students to make annotated drawings of their waves.
• Once students choose which waves they wish to document for their lab, they should annotate their sketches to identify wavelength, wave height, wave base, crest & trough.
• Finally, students should use their best measurements from their video still to calculate wave steepness and try to identify the type of wave. Not everyone will be able to capture the "perfect" wave setup, but everyone should be able to create some really neat waves!

Wrap up and share out (5 min)

• What types of breakers did student groups make in their bottles? Which is the most common in the class?

Extension Activity/Lab: Vortex Cannons (60-80 min)

In this extension activity/lab, students create a vortex cannon from a cardboard box and tape and analyze the motion of the wave pulse. The vortex cannon creates an entirely different-looking wave pulse, but students can still perform many of the same analyses that they've done in previous units. A note to instructors: Visualizing the wave pulse is impossible without the aid of dry ice, a fog machine, or incense. It's fine if the wave pulse is invisible (many real-world waves are!), but in that case you should omit the discussion question about the shape of the wave pulse.

Discussion Questions:

• How is the vortex cannon wave similar to the wave pulses that you made in previous activities? How is this wave pulse different?
• Does the shape of the hole form the shape of the wave pulse that exits the cannon, or is the wave pulse always the same shape? Is this similar to anything we've looked at before?
• Discuss your findings from your data – do they support your hypothesis? Or does your hypothesis need revision?
• Which SEPs (science and engineering practices) did you use today?

Whole-Class Wrap-Up (5-10 min):

• How would you draw the waves we looked at last week and today?
• How can we relate slinky and vortex cannon wave pulses to other waves we are (probably) more familiar with?

For the Vortex Cannons Lab:

• There are lots of ways to make a vortex cannon. This simple set-up only uses a balloon, scissors, and a plastic cup: youtube.com/watch?v=Ts6LXgZUxvc. A slightly more impressive cannon can be made with a larger balloon and a milk jug with the bottom cut off and covered with a balloon.
• Visualizing the waves with something (incense/smoke, dry ice, fog machine) is very helpful for the students - you can see that the vortex rings were always circles, and that wave speed didn't depend on the size of the pulse/amplitude or the shape of the hole, for example. Fog machines can be VERY prolific and if you're using a fog machine, this class might be best suited in a large classroom or outside. Smoke from burning incense is a lung irritant and should probably be done outside.

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).

There is an opportunity for as many as three science journals in this unit depending on which extension activities are completed. 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)

Reflections ask students to put their learning in their own words and also to apply their knowledge in a new and novel situation. As always, reflections should be about 500 words and they should both discuss content that reflects understanding and thoughtfully reflect on the materials.

Reflection prompt:

Open the PhET Simulation: Wave on a String, and spend 10-15 minutes experimenting with it.

What does this simulation tell you...

- That you already knew?

- That you did not know and found interesting/surprising?

We are wrapping up waves in this course and moving on to the next topic. What are some aspects and/or properties of waves that are consistent from one wave type to another? You can consider waves on a slinky, waves formed by the Hunga Tonga volcano, waves in the PhET simulation, and any other waves you can think of (either from class or outside of class). In what ways are they all similar?

Pre-Class reading assignments. Both of these reading assignments discuss basic properties of waves utilized in this unit:

• Waves and Wave Properties
• Waves and Wave Motion: Describing Waves

PhET simulation: Wave on a String. This simulation is used as a follow-up to the Slow Motion Slinky Wave Pulse Activity/Lab to help visualize properties of a wave pulse.

Waves and Wave Properties: This we bpage from the University of Hawaii provides valuable information relevant to the Pre-Class assignment.