Sound Travels Through Materials

Activities to try

1. 1

   Pick-a-medium sound bench (on-screen): swap the material between source and ear

   Why it works: Sound is a vibration that must be handed on through a material to reach the ear; solids and liquids carry it as well as air, and when the material is removed the sound stops - so a medium is required.

   1. Open the on-screen pick-a-medium interactive: a buzzing source (e.g. a bell or buzzer) on one side, an 'ear' on the other, and a gap you fill with a chosen material.
   2. Before each trial, predict out loud: 'Will I hear the buzz through this material - strongly, faintly, or not at all?' and say why.
   3. Drop air, then water, then wood, then a brick wall into the gap, and each time observe/listen whether the sound gets through and how its character changes (e.g. it can arrive strongly when the source and ear are in contact with a solid, and is still audible through water; a thick wall can also muffle sound that starts in the air).
   4. Then choose 'remove everything' to empty the gap into a vacuum on-screen, and observe that the sound cuts to silence because the vibration has nothing to travel through. (This on-screen removal is what makes the vacuum case testable - you cannot make a real vacuum at a desk, so the physical counterpart is the bell-in-a-jar demonstration.)
   5. State in your own words what the model showed (and what the real listening and bell-in-a-jar evidence supports): sound needs 'stuff' (a material) to travel through, and travels through solids and liquids as well as air, but not through empty space.
2. 2

   String telephone: taut carries well, slack carries poorly

   Why it works: Sound travels along a material path; the taut string itself vibrates along its length to carry the voice, while a slack string passes the vibration on poorly, so the sound becomes much fainter or is lost.

   1. Make a cup-and-string telephone and speak into one cup while a partner listens at the other with the string pulled taut.
   2. Then let the string go slack and try again, noticing that the voice becomes much fainter or cannot be heard.
   3. Explain the chain in order: your voice vibrates the first cup, the vibration runs along the taut string, it vibrates the second cup, which vibrates the air to your partner's ear.
   4. Explain why it fades when slack: the vibration travels along the string best when the string is pulled tight; a loose, floppy string does not pass the vibration on well, even though it still joins the cups.
3. 3

   Ear to the desk and listening through water (first-hand media)

   Why it works: Sound travels through solids and liquids as well as air - sometimes more clearly - so sound is not limited to air.

   1. Press your ear flat on a table and have a friend tap the far end of the table (not through the air) - listen and compare with hearing the tap through the air alone.
   2. Click two spoons together under the water in a bowl with your ear pressed against the side of the bowl, or listen to sounds while underwater, and notice the sound still reaches you through the water.
   3. For each, say which state of matter carried the sound (solid, liquid) and record an example of sound travelling through a solid, a liquid and a gas.