SIMPLE HARMONIC MOTION

BALL IN A BOWLPENDULUM

WATER WAVESSPRINGS

GUITAR STRINGSSOUNDLIGHT

WAVES

ONE DIMENSIONAL WAVES

CAN BE: PULSECONTINUOUSSTANDING

WAVES

LONGITUDINAL WAVESSLINKYSOUND

P-SEISMIC WAVES

TRANSVERSE WAVESSTRINGWATERLIGHT

S-SEISMIC WAVESOFTEN SINUSOIDAL (SINE WAVES)

MEASURES OF WAVES

AMPLITUDE: ENERGY IN THE WAVE

PERIOD: TIME BETWEEN PEAKS

FREQUENCY: CYCLES PER SECOND

SPEED = WAVELENGTH X FREQUENCY

WAVELENGTH: DISTANCE BETWEEN PEAKS

SPEED OF SOUND

• HOW WOULD YOU DESIGN AN EXPERIMENT TO MEASURE THE SPEED OF SOUND?

• WHAT FACTORS WOULD CONTRIBUTE TO EXPERIMENTAL ERROR?

HOW CLOSE WAS THAT LIGHTNING BOLT?

SOUND TRAVELS 700 mphin air at sea level

700 mph = 0.2 mps

Or: 5 second to travel one mile

How close was the lightning strike?Start counting off seconds after the bolt

until you hear the thunder (1 mile for every 5 sec).

INTERFERENCEWAVES WILL PASS THROUGH EACH OTHER WITHOUT PERMANENT EFFECT

THE MEDIUM MUST REACT TO THE SUM OF THE TWO (OR MORE) WAVES

IF THE PEAKS CORRESPOND: AMPLIFICATIONIF PEAK AND NODE CORRESPOND: REDUCTIONIF PEAK AND ANTI-PEAK CORRESPOND: A NODE

WHAT WOULD HAPPEN IF THERE WERE WAVE-MAKERS AT OPPOSITE ENDS OF THE WAVEPOOL?

SOUND IN A STRING

SPEED OF WAVE DEPENDS ON:

DENSITY OF STRINGCROSS-SECTION OF STRINGTENSION IN STRING

STANDING WAVES

SKIPPING ROPE

GUITAR STRING

TUNING A GUITAR STRING

CAN YOU HEAR THE BEAT?

STANDING WAVES

First harmonic

Second harmonic

Third harmonic

node

loop

WIND INSTRUMENTS

L = 3 0 /4

Flute, oboe, beer-bottle, organ...

DOPPLER SHIFT

WHEN A WAVE TRAVELS THROUGH A MEDIUMITS SPEED IS AFFECTED BY THE NATURE OF THAT MEDIUM. FOR EXAMPLE SOUND TRAVELS FASTER IN WATER OR STEEL THAN IN AIR.

IF THE SOURCE OF THE SOUND VIBRATION IS ALSO TRAVELLING THIS WILL AFFECT THE PITCH, OR FREQUENCY OF THE WAVE, SINCE THE PEAKS WILL BE CLOSER OR FURTHER APART.

DOPPLER SHIFT

SOURCE

LISTENER

SOURCE APPROACHING

SOURCE RECEDING

ENERGY IN WAVES

PARTICLES IN THE MEDIUM (STRING)MOVE AS THE WAVE PASSES

PE = 1/2 k x2

x is displacement

KE = 1/2 m v2

v = velocity or frequency

POWER IN WAVE = AMPLITUDE2

POWER IN WAVE = FREQUENCY2

BREAKING THE SOUND BARRIER

AS THE PLANE APPROACHES THE SPEED OF SOUND, WHAT HAPPENS THE SOUNDENERGY EMITTED BY THE PLANE IN A FORWARD DIRECTION?

CHANGE IN AMPLITUDE?CHANGE IN FREQUENCY?INCREASED ENERGY?

HEARING DECIBELS

VOLUME OF SOUND = 10 log (I/Io)

Whisper ~50 dbconversation ~ 70 dbpain threshold ~ 120 db

Like the Richter scale for earthquakes

2 bel is 10 times one bel,3 bel is 100 times one belone decibel is one bel/10

ELECTROMAGNETIC RADIATION

WHAT IS THE MEDIUM FOR LIGHT?

THE EM SPECTRUM IS MUCH WIDER THAN THE VISIBLE SPECTRUM

...GAMMA-X-UV-VISIBLE-IR-MICROWAVE-RADIO...

violet - blue - green - yellow - orange - red

SNELL’S LAW

a

a

mirror

a

OPTICS

SNELLS LAWMIRRORSPRISMS AND LENSES

REFRACTION

REFLECTION

n=1

n=1.33

air

glass

Light always finds the “least time” path

TWO DIMENSIONAL WAVES

WAVEFRONTS

DIFFRACTION AND INTERFERENCE

TWO-SLIT EXPERIMENT

INTERFERENCE FRINGES

COLOURS IN AN OIL-SLICK

ACTS LIKE A PRISM, IN REFLECTION

WAVES CONSTRUCTIVELY OR DESTRUCTIVELYINTERFERE WITH EACH OTHER

INTERFERENCE

DIFFRACTION GRATINGS

CAN ALSO GET INTERFERENCE FROM A REGULAR SPACED ARRAY OF LINES

OR AN ARRAY OF ATOMS IN A CRYSTAL

ONE-SLIT????

N+1-wavelengthsreinforcing

cancelling

N wavelengths reinforcing

cancelling

N+1/2 wavelengths

TWO-SLIT EXPERIMENT

CURVED MIRRORS

F

LENSES

LENSES (2)

INTERNAL REFLECTION

A

A’

C’

B’

B

C

Brewster’s angle

FIBRE OPTICS

CORE

CLADDING

n

n’ > n