Teacher Guide

Laser Dance Party

Experimenting with visual sound.

What do sound vibrations look like?

This resource was originally published in PhysicsQuest 2017: Sound.

This is the teacher guide for this lesson. A student-focused guide to assist learners as they perform the activity is available.

View the student guide: Laser Dance Party

What do sound vibrations look like?

  • Mylar square
  • Rubber band
  • 4 push pins
  • Binder clip
  • Laser
  • Rubber glove
  • MP3 download (see “Suggested Resources”)
  • Paper cup
  • Scissors
  • Music player (Smartphone, MP3 player, computer with external speaker, etc.)

N/A

  • Total time
    45 - 60 Minutes
  • Education level
    Grades 5 - 9
  • Content Area
    Sound
  • Educational topic
    Energy, sound waves, vibration

This whole PhysicsQuest kit has been about learning how different vibrations cause different sounds. We’ve looked at how size changes sound, how sound can be amplified, and how sound waves can interact. We’ve heard a whole lot of sounds. But we haven’t actually seen them.

We’ve learned that lower notes mean slower vibrations and louder sounds mean bigger vibrations, but it would be neat to actually see that. If sound is caused by vibrations, shouldn’t we be able to see those vibrations? We can see things vibrating, right?

Well, this whole activity is about actually seeing the sound. The problem with actually seeing the vibrations that create sound is that in a lot of cases things are vibrating too fast or too little. You can’t look at the little speakers in your headphones and see them vibrating.

There needs to be a way to visually amplify these vibrations and that’s where this activity comes in. In this activity, we are taking small vibrations — those from a smartphone or speaker — and using them to make something bigger and more elastic: the rubber glove. But the vibrations still aren’t quite big enough. To really be able to see the vibrations, we can reflect a laser off a vibrating rubber glove.

Think about playing with a cat with a laser pointer. If you haven’t done this, look up some videos of it on YouTube. I guarantee you won’t regret it. A small flick of the wrist causes the spot of the laser pointer to move a huge distance.

This is the same principle we are using for the experiment. When a laser pointer bounces off the mirror on the rubber glove, the vibrations move it a tiny amount. However, when the laser is moved just a little bit at the cup, you can see the laser spot move a lot more on the wall.

Students will actually see how the rubber glove is vibrating to cause the laser pointer to move and make patterns. The MP3 download from the PhysicsQuest site has different notes and different volumes. The goal is to have students really see how the rate of vibration, or frequency, changes when the pitch is changed. The lower notes will have slower vibrations and the higher notes may be vibrating so fast that it’s even hard to see in the laser pointer pattern.

They should also be able to see the difference in vibration amplitude as the volume is changed. The louder something is, the bigger the vibration. It’s going to be a lot easier to see the lower notes because the vibrations are much slower and our eyes have an easier time processing the movement.

I would highly recommend playing some fun music and seeing how the laser dances. Pick something loud with some great bass and the light show will be great.

Key terms

These are the key terms that students should know by the END of the two lessons. They do not need to be front loaded. In fact, studies show that presenting key terms to students before the lesson may not be as effective as having students observe and witness the phenomenon the key terms illustrate beforehand and learn the formalized words afterwards. For this reason, we recommend allowing students to grapple with the experiments without knowing these words and then exposing them to the formalized definitions afterwards in the context of what they learned.

However, if these words are helpful for students on an IEP, ELL students, or anyone else that may need more support, please use at your discretion.

  • Interference: When two waves hit each other, they interfere. Sometimes they add together, sometimes they cancel each other out.
  • Constructive Interference: When waves line up peak to peak and trough to trough, they make a bigger wave. This is constructive interference.
  • Destructive Interference: When waves are completely out of phase, peak to trough and trough to peak, they cancel out. This is destructive interference.
  • Beat frequency: When two waves of similar length interfere, they create a resulting wave that varies in intensity. The frequency with which it varies is called the beat frequency.
Objective

Students will experiment and explain what sound vibration looks like.

Before the experiment
  • Ask & Discuss

    What do you think sound would look like?

  • Use the turn & talk protocol
    1. Pair students up
    2. Give them a minute to think quietly
    3. Give students 2 minutes to discuss their thinking
    4. Have students record their answers or share out to the whole group
Setting up
  • Unscrew the battery

    Unscrew the battery compartment of the laser and remove the tiny piece of paper between the batteries. Screw the battery compartment back together.

  • Cut a horizontal slit

    Cut a horizontal slit in the paper cup about halfway between the lip and the bottom of the cup. The slit should be big enough to slip in a smartphone or other MP3 player or speaker.

  • Cut out the palm

    Cut out the palm of the rubber glove.

  • Put the rubber glove

    Put the rubber glove palm over the open end of the cup and hold it in place with the rubber band. It should look like a paper cup drum with a slip in the side.

  • Peel off the backing

    Peel off the backing from the Mylar square and stick it to the rubber glove, slightly off center.

  • Put the push pins

    Put the push pins in the side of the cup opposite the slit to make four little legs to support the cup.

  • Put the laser

    Put the laser in the binder clip so that the button is pressed by the edge of the binder clip. The laser is now on, so be very careful not to look directly at it.

  • Put the binder clip

    Put the binder clip and laser at the Mylar square so that it reflects off the Mylar.

  • Aim the reflection

    Aim the reflection at a wall. You should now have a laser projected on the wall. It might take some readjustments of the push pin legs to get everything to balance.

During the experiment
Collecting data
  • Make sure students

    Make sure students are put into intentional groups. See above.

  • Students will complete

    Students will complete the experiment using the Student Guide where we have outlined the experiment for students and along the way, they record results and answer questions.

Analyzing data
  • In the student guide

    In the student guide, they will answer questions that help them understand sound.

  • Continue to listen

    Continue to listen in on each group’s discussion, answer as few questions as possible. Even if a group is off a little, they will have a chance to work out these stuck points later.

Teacher tip

Suggested STEP UP Everyday Actions to incorporate into activity

  • When pairing students, try to have male/female partners and invite female students to share their ideas first
  • As you put students into groups, consider having female or minority students take the leadership role.
  • Take note of female participation. If they seem to be taking direction and following along, elevate their voice by asking them a question about their experiment.

Consider using white boards so students have time to work through their ideas and brainstorms before saying them out loud.

As students experiment, roam around the room to listen in on discussion and notice experiment techniques. If needed, stop the class and call over to a certain group that has hit on an important concept.

Consider using the RIP protocol (Research, Instruct, Plan) for lab group visits and conferring.

Consider culturally responsive tools and strategies and/or open ended reflection questions to help push student thinking, evidence tracking, and connections to their lives. Look for *** below to find suggested places to add.

Conclusion
  • Share-Trade protocol

    Share-Trade protocol to have students share and refine their thinking.

    1. Each student writes their individual thoughts for this question: If you wanted to make the most vibrant and impressive laser dance party, how might you do it?
    2. Students stand up with their ideas on paper and move around the room.
    3. Each student finds someone they don’t know very well and forms a partnership with them. To form a partnership, students must high five.
    4. With their partners, students share their ideas and trade papers.
    5. Each student is now responsible for sharing the ideas of the person they just spoke with, even if they don’t agree with those ideas. This isn’t a time for them to critique their partners’ ideas.
    6. Students form partnerships three or four times so they see and explain multiple ideas.
    7. Students return to their seats and write a final explanation or idea.
  • After students

    After students have had a chance to discuss key ideas from the lesson and complete their student guides, you can now clarify and give concise definitions to the forces they experimented with.

Credits

Created by Rebecca Thompson, Ph.D. and Monica Gallagher

Updated in 2023 by Sierra Crandell, M.Ed. partially funded by Eucalyptus Foundation

Extension by Jenna Tempkin with Society of Physics Students (SPS)

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