Introduction to Sound

Question:

Can sound be described as a wave?

Materials:

Instructions:

Instructions (Spatial Sound Wave Interference):

  1. Set up speakers ~ 1 ft apart, facing outwards in the same direction
  2. Connect to computer/smartphone
  3. Use frequency generator app to play low frequency (200-400 Hz) sound
  4. Walk around the room, listening for loud and quiet spots, representing maxima and minima in wave interference
    • Optional, use additional smartphone app (Da Tuner lite works well) to measure sound intensity in decibels to quantify maxima and minima
  5. When you find a quiet spot (minima), turn off or cover one of the speakers. The sound should increase since there is no longer any interference.
  6. Measure distance from speaker pair to maxima and minima to map the interference distribution

Instructions (Beat frequency Sound Wave Interference)

  1. Use same speakers, or internal stereo speakers of smartphone or computer
  2. Use two apps or videos to play nearly identical sound frequencies (eg. 500 and 501 Hz)
  3. Demonstrate they sound almost the same when played separately
  4. Play the two together to show the appearance of a difference (beat) frequency, equal to F2-F1
  5. Have the students time the beat frequency.  Try different frequencies with the same and different frequencies.

Instructions (Rubens Tube)

  1. Set up tube in area with minimal drafts/airflow. Even normal building AC can disrupt the flames
  2. Use small flow of propane and lighter to ignite flames spaced on the tube
  3. Use speaker to play lower frequency (~200 Hz) sound
  4. Adjust propane flow for stable, fairly low (several inches) flame height
  5. Adjust volume, frequency and speaker proximity to observe standing wave appearance of flames
  6. Finally, use speaker to play songs into tube, observing flame behavior to higher and lower frequency tones in the song.