Sound and Waves

Sound Waves

Mrs Wendt
Physics

What is Sound?

Sound: is a wave that is created by vibrating objects and propagated through a medium from one location to another.  It is a longitudinal wave.

Sound waves are similar except that they are much higher frequency and it is air that is being alternately compressed and expanded rather than the coils of a spring.

​How Sound Travels.

First, there is a medium that carries the disturbance from one location to another. 

Second, there is an original source of the wave, some vibrating object capable of disturbing the first particle of the medium. 

Third, the sound wave is transported from one location to another by means of particle-to-particle interaction.

​Pitch

Pitch: perceived frequency of sound. High pitch is high frequency and low pitch is low frequency.

The lowest frequency humans can ordinarily hear is a deep hum at a frequency around 20 Hz.

Even this frequency is so fast that you cannot see the vibration with your eye; instead, you can only see a slight blur.

Draw

Draw a Longitudinal Wave and label the rarefaction and the compression. Be sure to include at least one wavelength.

Multiple Choice

Waves that require a medium to travel are called:

• electromagnetic waves

• transverse waves

• longitudinal waves

• Mechanical waves

Loudness

The loudness of a sound depends on the amplitude of the wave. A loud sound has a larger amplitude than a soft sound of the same frequency. 

The loudness of a sound relates the intensity of any given sound to the intensity at the threshold of hearing.
It is measured in decibels (dB). The threshold of human hearing has an intensity of about .0000000000001 watts per meter squared and corresponds to 0 decibels. 

Intensity

Sound Intensity is defined as the sound power per unit area in a direction that is perpendicular to that area.

Intensity=Energy/(time x area) =  Power/Area

The distance vs. intensity is an example of the inverse square law

Drag and Drop

​

Placeholder

of Sound travels at ​

Placeholder

. ​

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is when you are moving faster than the speed of ​

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.

Drag these tiles and drop them in the correct blank above

343 m/s

Supersonic

sound.

Speed

frequency

Infrasonic

​Speed of Sound and Temperature

The speed of sound is affected by temperature in a given medium. For air at sea level, the speed of sound is given by

v_w=(v)√T÷273K,

where the temperature (denoted as T) is in units of kelvin.
The speed of sound in gases is related to the average speed of particles in the gas, v_rms and that:

v_rms=√3kT÷m.
k = 1.38 x 10^-23J/K
m = mass of the particles

Math Response

Air temperature in the Sahara Desert can reach 56.0ºC (about 134ºF). What is the speed of sound in air at that temperature? v=331 m/s

Type answer here

Correct Answer: 363.4

Deg^°

Rad

Doppler Effect

Doppler Effect: shift in frequency of a wave that is emitted from a source that is moving with respect to the observer.

There is an apparent upward shift in frequency for the observer and the source are approaching and an apparent downward shift in frequency when the observer and the source is receding. 

f= f_o(v_s/(v_s-v))

Math Response

An orchestral oboist sounds the note "A" at 440 Hz. If the speed of sound in air is 343 m/s, what is the wavelength of the note?

Type answer here

Correct Answer: 0.77

Deg^°

Rad

Open Ended

Giovanni is blind but his hearing has perfect pitch. How can he tell quickly if a marching band is marching toward or away from him?

Open Ended

Summarize the crash course video. Write down five facts you have learned from the video.

Multiple Choice

Types of Mechanical Waves

• Transverse Waves

• Longitudinal Waves

• Surface Waves

• All of the above

Multiple Choice

Human beings can normally hear sounds with a frequency of about:

• 10 and 10000 Hz

• 20 and 20000 Hz

• 20 and 140 Hz

• 10 and 120 Hz

Multiple Choice

A transverse wave moves from a medium A to a medium B. In medium A, the velocity of the transverse wave is 500 ms-1 and the wavelength is 5 m. The frequency and the wavelength of the wave in medium B when its velocity is 600 ms-1, respectively are

• 120 Hz and 5 m

• 100 Hz and 5 m

• 120 Hz and 6 m

• 100 Hz and 6 m

Drag and Drop

What is transferred from place to place by waves? ​

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​

Drag these tiles and drop them in the correct blank above

energy

matter

particles

light

Multiple Choice

If the amplitude increases, the energy of the wave:

• Increases

• Decreases

• Stays the same

Drag and Drop

If a wave has a greater frequency, what happens to the wavelength? ​

Placeholder

Drag these tiles and drop them in the correct blank above

increases

decreases

stays the same

Multiple Choice

The area of a longitudinal wave where particles are pushed close together are called:

• rarefactions

• compressions

• amplitude

• wavelength

Multiple Choice

Sounds waves can travel through space because they do not require a medium to travel.

• True

• False

Math Response

When poked by a spear, an operatic soprano lets out a 1200-Hz shriek. What is its wavelength if the speed of sound is 345 m/s?

Type answer here

Correct Answer: 0.29

Deg^°

Rad

Math Response

What frequency sound has a 0.10-m wavelength when the speed of sound is 343 m/s?

Type answer here

Correct Answer: 3430

Deg^°

Rad

Math Response

.

Calculate the speed of sound on a day when a 1500 Hz frequency has a wavelength of 0.221 m.

Type answer here

Correct Answer: 331.5

Deg^°

Rad