An Intro to WavesAn Intro to Waves

Hz are units of:Hz are units of:

A. amplitudeA. amplitude B. frequencyB. frequency

C. periodC. period D. wavelengthD. wavelength

In a sound wave, rarefactions are areas In a sound wave, rarefactions are areas of:of:

A. high amplitude A. high amplitude B. low amplitude B. low amplitude

C. high pressure C. high pressure D. low pressureD. low pressure

An Intro to WavesAn Intro to Waves

Hz are units of:Hz are units of:

A. amplitudeA. amplitude B. frequencyB. frequency

C. periodC. period D. wavelengthD. wavelength

In a sound wave, rarefactions are areas In a sound wave, rarefactions are areas of:of:

A. high amplitude A. high amplitude B. low amplitude B. low amplitude

C. high pressure C. high pressure D. low pressureD. low pressure

An Intro to WavesAn Intro to Waves

Hz are units of:Hz are units of:

A. amplitudeA. amplitude B. frequencyB. frequency

C. periodC. period D. wavelengthD. wavelength

In a sound wave, rarefactions are areas In a sound wave, rarefactions are areas of:of:

A. high amplitude A. high amplitude B. low amplitude B. low amplitude

C. high pressure C. high pressure D. low pressureD. low pressure

Sound Speed and Sound Speed and Frequency:Frequency:

Learning GoalLearning GoalThe student will be able to explain the The student will be able to explain the

nature between the speed of sound nature between the speed of sound in various media and the particle in various media and the particle nature of the media and explain nature of the media and explain selected natural phenomena selected natural phenomena (echolocation, (echolocation, infrasound/ultrasound) with infrasound/ultrasound) with reference to the characteristics and reference to the characteristics and properties of waves (E3.5, E3.6).properties of waves (E3.5, E3.6).

Sound Speed and Sound Speed and FrequencyFrequency

3U Physics3U Physics

The Speed of a WaveThe Speed of a Wave

As demonstrated by the slinky waves, As demonstrated by the slinky waves, the speed at which a wave the speed at which a wave propagates is dependent on the propagates is dependent on the properties of the medium.properties of the medium.

Sound WavesSound Waves

Remember that Remember that sound is a sound is a pressure wavepressure wave. A . A vibration (e.g. of a vibration (e.g. of a tuning fork) bumps tuning fork) bumps air particles, which air particles, which bump the air bump the air particles next to particles next to them, etc. them, etc.

Sound in AirSound in Air

Sound travels faster in warmer air (in Sound travels faster in warmer air (in which the particles are faster-which the particles are faster-moving):moving):

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Sound in Air: ExampleSound in Air: Example

ExampleExample: You see a flash of lightning : You see a flash of lightning from a storm 1.4 km away and hear from a storm 1.4 km away and hear the crack of lightning 4.0 s later. the crack of lightning 4.0 s later. What is the temperature of the air?What is the temperature of the air?

Sound in Air: ExampleSound in Air: Example

ExampleExample: You see a flash of lightning : You see a flash of lightning from a storm 1.4 km away and hear from a storm 1.4 km away and hear the crack of lightning 4.0 s later. the crack of lightning 4.0 s later. What is the temperature of the air?What is the temperature of the air?

Sound in Air: ExampleSound in Air: Example

ExampleExample: You see a flash of lightning : You see a flash of lightning from a storm 1.4 km away and hear from a storm 1.4 km away and hear the crack of lightning 4.0 s later. the crack of lightning 4.0 s later. What is the temperature of the air?What is the temperature of the air?F irst find the speed o f sound in a ir

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Sound in Air: ExampleSound in Air: Example

ExampleExample: You see a flash of lightning : You see a flash of lightning from a storm 1.4 km away and hear from a storm 1.4 km away and hear the crack of lightning 4.0 s later. the crack of lightning 4.0 s later. What is the temperature of the air?What is the temperature of the air?F irst find the speed o f sound in a ir

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Sound in Air: ExampleSound in Air: Example

ExampleExample: You see a flash of lightning : You see a flash of lightning from a storm 1.4 km away and hear from a storm 1.4 km away and hear the crack of lightning 4.0 s later. the crack of lightning 4.0 s later. What is the temperature of the air?What is the temperature of the air?

Sound in Air: ExampleSound in Air: Example

ExampleExample: You see a flash of lightning : You see a flash of lightning from a storm 1.4 km away and hear from a storm 1.4 km away and hear the crack of lightning 4.0 s later. the crack of lightning 4.0 s later. What is the temperature of the air?What is the temperature of the air?

Sound in Air: ExampleSound in Air: Example

ExampleExample: You see a flash of lightning : You see a flash of lightning from a storm 1.4 km away and hear from a storm 1.4 km away and hear the crack of lightning 4.0 s later. the crack of lightning 4.0 s later. What is the temperature of the air?What is the temperature of the air?

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Sound in Liquids and Sound in Liquids and SolidsSolids

And sound will also travel faster in And sound will also travel faster in denser materials (liquids and solids).denser materials (liquids and solids).

E.g. the speed of sound in water is E.g. the speed of sound in water is typically 1500 m/s.typically 1500 m/s.

Sound in Liquids and Sound in Liquids and SolidsSolids

And sound will also travel faster in denser And sound will also travel faster in denser materials (liquids and solids).materials (liquids and solids).

E.g. the speed of sound in water is E.g. the speed of sound in water is typically 1500 m/s.typically 1500 m/s.

A swimmer 1500 m away from a loud A swimmer 1500 m away from a loud sound would hear it the sound 1 s later sound would hear it the sound 1 s later through the water or more than 4 s later through the water or more than 4 s later through the air.through the air.

Echolocation: ExampleEcholocation: Example

ExampleExample: A dolphin sends out a pulse : A dolphin sends out a pulse at a frequency of 100 000 Hz and at a frequency of 100 000 Hz and hears an echo back from an object hears an echo back from an object 2.4 s later. How far away is the 2.4 s later. How far away is the object?object?

Echolocation: ExampleEcholocation: Example

ExampleExample: A dolphin sends out a pulse : A dolphin sends out a pulse at a frequency of 100 000 Hz and at a frequency of 100 000 Hz and hears an echo back from an object hears an echo back from an object 2.4 s later. How far away is the 2.4 s later. How far away is the object?object?

Echolocation: ExampleEcholocation: Example

ExampleExample: A dolphin sends out a pulse : A dolphin sends out a pulse at a frequency of 100 000 Hz and at a frequency of 100 000 Hz and hears an echo back from an object hears an echo back from an object 2.4 s later. How far away is the 2.4 s later. How far away is the object?object?

Echolocation: ExampleEcholocation: Example

ExampleExample: A dolphin sends out a pulse : A dolphin sends out a pulse at a frequency of 100 000 Hz and at a frequency of 100 000 Hz and hears an echo back from an object hears an echo back from an object 2.4 s later. How far away is the 2.4 s later. How far away is the object?object?

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FrequencyFrequency

The frequency of The frequency of any sound wave is any sound wave is always the frequency of the source always the frequency of the source and does and does not not changechange or affect the or affect the speed of the wave as it propagates.speed of the wave as it propagates.

Frequency of a wave is how many cycles/peaks pass a point in a second

FrequencyFrequency

The frequency of The frequency of any sound wave is any sound wave is always the frequency of the source always the frequency of the source and does and does not not changechange or affect the or affect the speed of the wave as it propagates.speed of the wave as it propagates.

(Changing the speed will change the (Changing the speed will change the wavelength, not the frequency.)wavelength, not the frequency.)

WavelengthWavelength

Distance between two similar points Distance between two similar points in successive identical cycles in a in successive identical cycles in a wavewave

The Wave EquationThe Wave Equation

How are frequency, wavelength and How are frequency, wavelength and velocity of a wave connected?velocity of a wave connected?

V=d/t, we can substitute V=d/t, we can substitute λλ for d, so V= for d, so V= λλ/t and t is the period of a wave, T /t and t is the period of a wave, T thereforetherefore

V=V= λ λ/T/T

V=V= λ λff

FrequencyFrequency

Humans can hear sounds between about Humans can hear sounds between about 20 and 20 000 Hz (though most humans 20 and 20 000 Hz (though most humans lose the ability to hear very high lose the ability to hear very high frequencies by the time they are frequencies by the time they are teenagers).teenagers).

Most human speech is between 200 and Most human speech is between 200 and 8000 Hz, and the ear is most sensitive to 8000 Hz, and the ear is most sensitive to frequencies between 1000 and 3500 Hz.frequencies between 1000 and 3500 Hz.

UltrasoundUltrasound

Sound above 20 Sound above 20 000 Hz is called 000 Hz is called ultrasoundultrasound..

A common use of A common use of ultrasound is ultrasound is range finding range finding under water: i.e. under water: i.e. echolocation or echolocation or sonar.sonar.

UltrasoundUltrasound

Diagnostic medical ultrasonograms work on Diagnostic medical ultrasonograms work on the same principle.the same principle.

InfrasoundInfrasound

Sound below 20 Hz is Sound below 20 Hz is called infrasound, called infrasound, which may be which may be produced by events produced by events such as earthquakes.such as earthquakes.

Some animals such as Some animals such as elephants use elephants use infrasound for infrasound for communication, even communication, even over long distance.over long distance.

InfrasoundInfrasound

While humans cannot consciously While humans cannot consciously detect infrasound, they may still detect infrasound, they may still be sensitive to the vibrations:be sensitive to the vibrations:

In particular, infrasound is known In particular, infrasound is known evoke feelings of awe and fear, evoke feelings of awe and fear, and frequencies close of 18 Hz, and frequencies close of 18 Hz, the resonant frequency of the the resonant frequency of the eye, may cause optical illusions eye, may cause optical illusions of “ghosts.” Infrasound may be of “ghosts.” Infrasound may be responsible for many alleged responsible for many alleged “hauntings.”“hauntings.”

Frequency and PitchFrequency and Pitch

Within the audible range, Within the audible range, frequency of a sound frequency of a sound wave is commonly wave is commonly referred to as the referred to as the pitchpitch of the sound. of the sound.

A high-frequency sound A high-frequency sound wave has a high pitch.wave has a high pitch.

A low-frequency sound A low-frequency sound wave has a low pitch.wave has a low pitch.

Frequency and NoiseFrequency and Noise

A sound wave of a single frequency A sound wave of a single frequency will be heard as a distinct tone or will be heard as a distinct tone or note.note.

Irregular sound waves will be heard Irregular sound waves will be heard as as noisenoise..

More PracticeMore Practice

Sound Speed Quick LabSound Speed Quick Lab

Homework: Sound Speed and Homework: Sound Speed and FrequencyFrequency