Fourth Grade

Secret Bells – Sound Waves Experiment

by Anderson

Question to Explore

Do metal objects sound louder or quieter with your ears plugged?

Materials

  • wire hanger
  • 3 foot long piece of string
  • metal washer
  • metal spoon
  • wrench
  • table leg or side of table

Procedure

First, students created their instrument:

  1. Cut a piece of string 3 feet long.
  2. Hold the two ends of the string in one hand. The rest will make a loop.
  3. Lay the loop over the hook part of the wire hanger. Push the two ends through the loop, and pull them all the way through the other side.
  4. Wrap the loose ends of the string two or three times around the first fingers on each hand.
  5. Predict what it will sound like when you bump the hanger against the leg of a table with your ears open and with your ears plugged.

Test it out!

  1. Swing the hanger so it gently bumps the leg of a table. Record what it sounded like
  2. Next, Put your hands over the openings of your ears and bump the metal object. Record what it sounded like.
  3. Place other objects on your string and do the same test. Compare the sounds of each object. Some options include: a metal spoon, a metal washer, a wrench
  4. Record your observations and write your claim. Why do you think these objects sound the way they do?

Observations/Results

Most students predicted that the sound would be much fainter with their ears plugged. However, the opposite proved to be true! The sound was much louder and deeper when our ears were plugged. Many students compared it to the sound of a church bell. After testing this out with a few other metal objects, students made a claim as to why this happens. Students learned that when our hands are over our ears, more of the sound vibrations can reach our ears. Instead of traveling from solid to air, and back to solid, the sound is moving from one solid (the string) to another (our bones), and then into the fluid in our cochlea.

Resources

We began by watching this video about how sound travels:

https://www.youtube.com/watch?v=gdGyvGPZ1G0

 

Here is where I got the idea for the lesson:

https://www.exploratorium.edu/science_explorer/secret_bells.html

 

This is a graphic organizer I created for students to record their observations:

Sound energy