Sound as a Wave

What happened to the Tacoma Narrows Bridge?

Wind blowing through a canyon resonates the natural frequency of the bridge.The wind was a periodic force acting on the bridge and increased the amplitude

This is an example of constructive interference

http://images.businessweek.com/ss/08/10/1006_tacoma_narrows/index.htm

What is constructive interference?

When two waves interact increasing the amplitude

*wave on a string animation

What is destructive interference

When two waves interact and decrease amplitude, or sometimes cancel out

What is sound?

Longitudinal wave through a medium that vibrates eardrum

    Our medium is air, unless we are underwater

    How does that sound differently?

Properties of a sound wave

Frequency: determines pitch, measured in Hz

(pitch: is highness or lowness of sound)

Amplitude: determines loudness, measured in decibels (dB)

*sound animation

*wave interference animation

Sound quiz!

Which is the: highest, loudest, lowest, quietest?

http://www.cleantechtutor.com/images/wave.png

http://www.cleantechtutor.com/images/wave.pnghttp://www.cleantechtutor.com/images/wave.pnghttp://www.cleantechtutor.com/images/wave.pnghttp://www.cleantechtutor.com/images/wave.png

http://www.cleantechtutor.com/images/wave.png

Velocity of sound wave

In air at normal temperature, the velocity of a sound wave is 340 meters per second

The speed of light is 300 million meters per second (300,000,000 m/s)

Supersonic: anything faster than 340 m/s

Subsonic: anything slower than 340 m/s

 

 

Changing velocity of sound

Change velocity of sound by changing density of medium

(the medium is the stuff through which a wave flows)

ex. Whales communicating across ocean

 

 

Destructive interference and beats

Beats: repeating change in amplitude caused by two waves of similar frequency interfering with each other

Good sounding sounds

Consonance: when sounds interact in a way that sounds nice

Dissonance: when sounds interact and it sounds bad

http://www.kirksville.k12.mo.us/khs/Teacher_Web/alternative/sound_noise_wave.JPG

How to change pitch

1)                      Change frequency

2)                      Object making noise moves

 

 

Doppler effect

The heard change in pitch as moving object makes noise

http://images.yourdictionary.com/images/science/ASdopple.jpg

*Police siren animation

*Doppler effect animation

How do we hear frequency?

All animals have different ranges of frequency they can hear

Ex 1: humans canít hear dog whistles

Ex 2: giraffes communicate at a lower frequency that we can hear

What frequencies can people hear?

Letís make a histogram