12/16/08

Post date: Dec 15, 2008 9:14:30 PM

Bell Activity: How does the flame tube support the idea of sound being changes in pressure?

• • Flame tube demonstration - video to come

  • Pitch and loudness

    • We hear the frequency of a wave as pitch

      • We are only sensitive to frequencies from about 20 Hz to about 16,000 Hz

    • The amplitude of the wave (how much the pressure varies) determines how loud it sounds to us

      • We can detect a pressure change of less than a billionth of an atmosphere of pressure (2 x 10^-5 Pa)

      • Noise begins to get painful at a million times that amplitude (20 Pa)

      • Measure sound loudness in decibels (dB)

        • Not a linear scale

        • If a sound's intensity goes up by 10 dB, it sounds twice as loud to us

  • The Doppler Effect

    • The speed and direction of a sound source impact how we hear it's frequency

    • http://www.kettering.edu/~drussell/Demos/doppler/doppler.html for some cool animations!

    • When a sound source is moving toward a listener, the listener hears a higher pitch. If it is moving away from the listener, the listener hears a lower pitch. Click the image below to see an animation of this.

• • • Can use the Doppler Effect to determine the speed of an object

      • Sonar in submarines

      • Bats to catch insects

      • Red shift in telescopes - universe is expanding at an increasing rate!

• • How we create and change sounds

    • Create sounds with vibrations

    • All objects have certain frequencies they tend to vibrate at

    • Can change those frequencies through a variety of methods

    • Blue Man Group video