Sine Curve

• Pictorial representation of a wave

Mechanical Waves

• Requires a medium– Cannot travel through empty space

(in a vacuum)

• Ex. Water waves, sound

Electromagnetic Waves

•Do NOT require a medium - can move through empty space (a vacuum)

•Ex. Radio waves, light waves, microwaves, x-rays

WAVES

•Transfer energy not matter from one place to another

•Disturbance that moves through space or through a medium (material)

TRANSVERSE WAVESParticles vibrate perpendicular to

the wave motionTransverse waves can be polarized

string musical instruments

ripples on water

electromagnetic waves e.g. Light waves, x-rays, radio waves

Picture of a Transverse Wave

CrestCrest

TroughTrough

WavelengthWavelength

AA

A - AmplitudeA - Amplitude

Transverse Wave

http://dev.physicslab.org/Document.aspx?http://dev.physicslab.org/Document.aspx?doctype=3&filename=WavesSound_IntroductionWaves.xmldoctype=3&filename=WavesSound_IntroductionWaves.xml

Longitudinal Wave

• Compression- (similar to crests) – particles close together (high density)

• Rarefactions (similar to troughs)- particles spread out or rarefied (low density)

Sound

• Travels as a longitudinal wave

• sounds audible to humans range from 20 - 20,000 Hz

• as f increases, pitch rises

LONGITUDINAL WAVESParticles vibrate parallel to the motion

of the waves

Ex: Sound Waves

http://dev.physicslab.org/Document.aspx?doctype=3&filename=WavesSound_IntroductionWaves.xmlhttp://dev.physicslab.org/Document.aspx?doctype=3&filename=WavesSound_IntroductionWaves.xml

SOUND FREQUENCY• Determines pitch

– frequency and pitch are directly related

• 20-20,000 Hz are audible to avg. person

• < 20 Hz are infrasonic

• > 20,000 Hz are ultrasonic

What is the Mosquito Ring tone?

• High pitched ring tone that most adults cannot hear

• “teen buzz”

• originally designed as a repellant

• Mosquito ringtone is 17 kHz (that’s 17,000 Hz for those of you who forgot what a kilo is)

• The highest note on a piano is only 4 kHz

Hearing Range by Age

16

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

18-21 yrs 30-39 yrs 40-49yrs 50-59 yrs

Hearing

Range

kHz

2-16 kHz 2-14

kHz 2-12 kHz 2-11

kHz

Frequencies

• http://www.opti.dyndns.org/~dng/SOUND/ReferenceSound/refsound.html

• http://www.freemosquitoringtone.org/

Ringtones

DOG IN WATER

Dog treads water (no velocity)

Dog swims to the right

Dog swims at same speed as water waves he is creating

Doppler Effect

• A change in frequency due to a change in motion of either the vibration source or the observer

• Objects in motion compress the light waves in front of them making them appear more blue (blue shift), the light waves behind are stretched out and appear more red (red shift).

http://cse.ssl.berkeley.edu/bmendez/ay10/2002/notes/lec8.html

Reflection

• Turning back of a wave at the boundary of a new medium

• ex. Light off a mirror; sound echo

Tacoma Narrows Bridge

• Why did the Tacoma Narrows Bridge fall?

Video of bridge: Video of bridge: http://www.archive.org/stream/SF121/SF121_256kb.mp4

Tacoma Narrows Bridge• Collapsed Nov 7, 1940• The failure of the

bridge occurred when a never-before-seen twisting mode occurred. This is called a torsional mode whereby when the left side of the roadway went down, the right side would rise, and vice-versa, with the centerline of the road remaining still.