You’ve spent three activities learning about how sound works. You’ve heard all sorts of interesting things make noise. You know that sound is caused by vibrations and that sound travels as a wave. All this investigation has been done with your ears. In this activity you’ll be able to use a laser to actually see the vibrations that make sound.
Student Guide
Laser Dance Party
Experimenting with visual sound.
What do sound vibrations look like?
This resource was originally published in PhysicsQuest 2017: Sound.
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.)
Intro
Before the experiment
What is the sound?
- Draw what you think
Draw what you think sound would look like if you could see it.
- Think loud v soft
- Lower v higher
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
- Pick your favorite song
Pick your favorite song with lots of bass and get it ready to play on your MP3 player.
- Put the MP3 player
Put the MP3 player or speaker in the hole you cut in the cup. This may be a bit of a balancing act. Once you have it balanced, make sure the laser is still pointing at the wall.
- Hit “play”
Hit “play” and watch the laser.
- What happened?
- Now pick a song
Now pick a song with less bass and more treble and hit “play.”
- How was the laser’s movement different?
- Download the MP3
Download the MP3 from _______________.
- Use the same setup
Use the same setup as in the qualitative section - only this time use the MP3 instead of your favorite tune.
- Set the volume
Set the volume in the middle of your MP3 player’s range.
- Hit “play”
Hit “play.” You will hear a series of pitches. The file will tell you the frequency of each pitch.
- Record what happens
Record what happens to the laser with each frequency/pitch.
- Increase the volume
Increase the volume to ⅔ of your MP3 player’s range. Repeat steps 4 and 5.
- How does the laser movement you see compare to the movement when the volume was set at the middle of your MP3 payer’s range?
- Set the volume at max
Set the volume at max and repeat steps 4 and 5.
- How does the laser movement you see compare to the movement when the volume was set at the middle of your MP3 payer’s range?
- When it was set at ⅔ of the range?
Analyzing data
- Why did the laser move?
Why did the laser move?
- When did it move
When did it move the most?
- How were low notes
How were low notes different from higher notes?
- Why?
- How did the volume
How did the volume affect the laser?
- Why?
- Do you think
Do you think you could get the laser to move in a specific pattern if you wanted to?
- How?
Conclusion
- If you wanted
If you wanted to make the most vibrant and impressive laser dance party, how might you do it?