• Tuning fork in water: what does this show?  The tuning fork VIBRATES.  Sound is always caused by something

 

 
 
 

What does our mental model of pressure tell us about what a vibrating object does when it is in the air?
 
 

• Door-window example:  I open the door and paper held in front of an open window moved out. What made that happen?

• Drum and paper fringe

 

• Tuning fork in air

• Slinky:  this models a longitudinal compression wave analogous to one compression in a sound wave (the arms of a tuning fork 'whapping' the air once).  Compressing the rings on the slinky with a sharp push sends a pulse down the line.

• People in a line model

Speed of sound is 330 meters/second or 740 miles/hour in air.
It needs some medium and travels better in liquids and solids.

• See bat hit before hearing it:  why?  How is this related to why you see lightening and then hear the thunder it produces?

• Tea party underwater

• Oven rack

• Bell in vacuum jar

Sound can be reflected and/or absorbed (turned to heat).

• Echo:  why does an echo occur?

• Sound proof booth:  what material would you hang on the walls to reduce any echo?

Natural frequency:  the special frequency at which an object vibrates.  Bigger, more massive things tend to vibrate slower and produce a lower pitch.

• Straw clarinet

• Blowing over a Coke bottle

• Guitar

• Wine glass hum

Some things to research (not covered in class or included on the test):

Doppler effect: the apparent change in pitch when an a sound source is moving toward you (raised pitch) or away from you (lower pitch)

• Swinging the bell

• Vroom of passing truck

Sonic boom!