What Does It Matter?

What You Need:

  • 3 plastic sealable bags
  • Sand (sugar or flour can be substituted)
  • Water
  • Coin

What You Do:

  1. Fill the first bag halfway with sand. Push out the extra air and seal the bag shut.
  2. Fill a second bag halfway with water. Again, push out the extra air and seal the bag shut. Make sure that it doesn't leak.
  3. Fill a third bag halfway with air. Seal it and place all three bags on the tabletop.
  4. Place your ear on the bag of sand. Gently tap a coin on the tabletop. What do you hear?
  5. Repeat the coin tapping while listening through the bag of water. Does it sound the same? How has the tapping sound changed?
  6. Repeat the tapping one more time while listening through the bag filled with air. Compare the three sounds.

What Happened?

Sounds are transferred by particles that slam into neighboring particles. Solids contain particles with the closest neighbors. Next comes liquids. Gases have the most spread-out particles. The closer the particles are to each other, the better the sound transmission. That's why the sound that passed through the solid and liquid may have seemed much louder than the sound that passed through the air-filled bag.

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