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