See the sound

Sound is produced when an object vibrates and creates a sound pressure wave that moves through a medium (i.e. solid, liquid or gas). As the pressure wave propagates from the sound source, the energy from it causes particles in the surrounding medium to vibrate and bump into other neighboring particles, initiating a chain reaction of particle movement as the sound is transmitted. While we can’t see the particles vibrate, we can sometimes feel the vibrations. 

The following activity will allow students to observe sound vibrations. 

Instructions

  1. Cover the opening of the bowl with cling wrap. Make sure it is very taut, like a drum. You can use a rubber band to secure the cling wrap.
  2. Place a few grains of rice (or any other small particle item you are using) on the cling wrap.
  3. Place the sound source as close to the bowl as possible.
  4. Make some sound! The students should be able to see the rice grains moving on the plastic when sound is produced. 
  5. Once the rice is moving, experiment by slowly moving the sound source away. What happens?
  6. Explore with different volumes and frequencies of sound to observe varying effects on the movement of the rice. You can also experiment with different sources of sound, such as a drum, humming, or even placing your speaker inside the bowl, if it fits!

What’s happening

As sound travels outwards from its source, it causes the surrounding air particles to vibrate. With sufficient energy, these vibrations extend to the rice particles, setting them in motion. The closer and louder the sound source is to the object, the more visible these vibrations in the rice will be. 

Wrap-up questions

  1. If using different sound sources, which one worked the best?
  2. Describe what happened as you moved the sound source closer or further to the bowl.

Why is this important?

Understanding how sound is produced, propagated and received is important as we investigate how noise pollution may impact various species. Although not every species possesses the ability to ‘hear’ sound, they all perceive it in some form. Given that sound travels faster and further underwater than in air, noise pollution in the oceans poses a particularly significant threat to marine species.

Materials

  • Bowl
  • Rubber band (optional)
  • Cling wrap
  • Sound source: a speaker works best, alternatively you can use your voice and hum
  • Rice (or some other small particle item like sprinkles)

Video: For a material-free alternative, play this video

https://www.youtube.com/watch?v=BoeDI-YkzI0

Estimated time

5 minutes