Sound and Wave Interference

Sound Waves

Sound is a compressional wave which travels through the air through a series of compressions and rarefactions.

Sound travels through different media.

Sound travels different speeds in different media. Sound typically travels faster in a solid that a liquid and faster in a liquid than a gas.

The denser the medium, the faster sound will travel.

The higher the temperature, the faster the particles of the medium will move and the faster the particles will carry the sound.

What is sound intensity?

Sound intensity is the energy that the sound wave possesses. The greater the intensity of sound the farther the sound will travel and the louder the sound will appear.

Loudness is very closely related to intensity. Loudness is the human perception of the sound intensity. The unit for loudness is decibels.

Loudness in Decibels

How is frequency related to pitch?

The pitch of a sound wave is directly related to frequency. A high-pitched sound has a high frequency (a screaming girl). A low-pitched sound has a low frequency (a fog-horn).

A healthy human ear can hear frequencies in the range of 20 Hz to 20,000 Hz. Humans cannot hear below 20 Hz. Sounds below this frequency are termed infrasonic.

Sounds above 20,000 Hz are termed ultrasonic. Some animals, such as dogs, can hear frequencies in this range in which humans cannot hear.

Different sounds that you hear include (A) noise, (B) pure tones, and (C) musical notes.

All Shapes of Waveforms

Different Instruments have Different Instruments have different waveformsdifferent waveforms a: glockenspiela: glockenspiel b: soft pianob: soft piano c: loud pianoc: loud piano d: trumpetd: trumpet

Our ears are sensitive to the Our ears are sensitive to the detailed shape of waveforms!detailed shape of waveforms!

More waveforms:More waveforms: e: french horne: french horn f: clarinetf: clarinet g: violing: violin

The ear assesses frequency content

The exact mixture of frequency content is The exact mixture of frequency content is how we distinguish voices from one anotherhow we distinguish voices from one another effectively, everyone has their own effectively, everyone has their own

waveformwaveform and corresponding spectrumand corresponding spectrum though an “A” may sound vastly similar, though an “A” may sound vastly similar,

we’re sensitive to very subtle variationswe’re sensitive to very subtle variations

Wave Interference

When two wave pass each other their superpositionWhen two wave pass each other their superposition

causes reinforcement or cancellation.causes reinforcement or cancellation.

Interference

Constructive interferenceReinforcement when the crest of one wave Reinforcement when the crest of one wave

overlaps the crest of another overlaps the crest of another Their individual effects adds together, Their individual effects adds together,

resulting in a wave increased in amplituderesulting in a wave increased in amplitude

Destructive InterferenceCancellation when crest of one wave Cancellation when crest of one wave

overlaps trough of another reducing their overlaps trough of another reducing their individual effects.individual effects.

Sound Wave Interference

•Interference occurs when two sounds of different frequenciesare heard superposed. •Constructive interference causes louder sound and destructive inference cause fainter sound.•This alternating pattern produces a beat. A piano tuner listens for beats to disappear.

Water Wave Interference

Left side is theoretical drawing of an interference Left side is theoretical drawing of an interference pattern.pattern.

Right side is the actual interference pattern.Right side is the actual interference pattern.

Standing WavesOccurs when a wave reflects upon itself and interferes Occurs when a wave reflects upon itself and interferes

with itself, making it appear to be still. with itself, making it appear to be still. Nodes remain stationary Nodes remain stationary

Anti nodes-occur half way between nodesAnti nodes-occur half way between nodes

Standing WavesChange the frequency in a standing wave and more nodes/antinodes appear in the event

DOPPLER EFFECT

Refers to the change in frequency when there is relative motion between an observer of waves and the source of the waves

Doppler with SoundDoppler with Sound

Doppler with Water

The Doppler effect-

Stationary bug Stationary bug

Bug swimmingBug swimming

Blue Shift-increase in frequency Blue Shift-increase in frequency Red Shift- Decrease in frequencyRed Shift- Decrease in frequency

Doppler Shift Gives Radial Velocity

Radar

True Velocity

Tangential Velocity

Radial Velocity

Compare these spectra.Compare these spectra.

Spectrum of Hydrogen in Lab

Spectrum of Star

What do these spectra tell us about the star?

Bow waves

V-shaped pattern made by overlapping crestV-shaped pattern made by overlapping crest

Shock Waves Produced by supersonic aircraft, Produced by supersonic aircraft,

three-dimensional cone shapedthree-dimensional cone shaped Sonic boom – sharp crack heard Sonic boom – sharp crack heard

when conical shell of when conical shell of compressed air that sweeps compressed air that sweeps behind a supersonic aircraft behind a supersonic aircraft reaches listeners on the ground reaches listeners on the ground below.below.

Supersonic

- slower than the speed of soundSubsonic

Supersonic - faster than the speed of sound

Mach Number =speed of soundspeed of object