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