10/31/08

Post date: Oct 31, 2008 2:28:14 AM

Bell Activity: (referring to a laser bouncing off a speaker) Why does the laser move around so much? What does this tell us about how a speaker works?

• • Wave speed

    • Depends on what type of wave

    • Depends on properties of the medium

      • molecules that are closer together transmit waves faster

      • Gases - farthest apart, so slowest waves

      • Liquids - closer together, so faster waves

      • Solids - closest together, so fastest waves (try tapping on desk with ear pressed to it... do you hear it better with your ear to the table or the one that's not on the table?)

    • Light has definite speed = 300,000,000 m/s in a vaccuum.

  • Doppler effect

    • Waves move at a certain speed, regardless of how fast the wave source is moving

      • Waves ahead of source get squeezed together for a higher pitch, waves behind get spread apart for lower pitch

    • Page 522 for picture and explanation

    • Example - Moving chimes

  • Sound waves

    • Vibrations in the air

    • The wave shape represents pressure, or density

      • Changes in pressure seen with spinning sound tubes sucking up bits of paper (also can be used to demonstrate Doppler effect)

    • Longitudinal waves

    • Frequency is related to what we hear as pitch

      • Order tuning forks from lowest pitch to highest pitch - check frequencies

    • Sound created depends on a variety of factors with instruments

      • What material

      • How vibration is made

      • Playing technique

      • Example - banjo

      • Example - Blue Man Group DVD

• Homework: Page 523:1-9 due monday