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Waves and Sound.

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Waves and Sound

Waves Are disturbances that move through an empty space or through medium (atoms and molecules) Waves transfer energy without transferring matter. Particles of medium move in simple harmonic motion Mechanical: Through a medium Electromagnetic: Through empty space

Two types of mechanical waves that require a medium
Caused by a disturbed medium and move by action reaction of particles ex: water wave, sound A medium is matter particles like gas (ex. air), liquid (ex. Water), and solid (ex. earth) Two types of mechanical waves that require a medium Transverse Wave Longitudinal Wave

Electromagnetic wave: Move through empty space (no medium)
Created by moving electrons Ex. radio waves, microwaves, light Types Electromagnetic Waves Through empty space

In order to start and transmit a wave, a source of disturbance (vibration) and a disturbed medium or electron are required. Mechanical caused by vibrating particles Electromagnetic by vibrating electrons

Section 2: Types of Mechanical Waves
Transverse Longitudinal

Wave particles move perpendicular to the direction the wave travels
Perpendicular to the direction of travel Direction of travel Transverse Wave: Wave particles move perpendicular to the direction the wave travels Ex. vibrating string of a musical instrument

Crest- highest point on a transverse wave
Trough- lowest point on a transverse wave Equilibrium position- center around which simple harmonic motion occurs Amplitude- from the equilibrium position to the crest or trough

Particles vibrate parallel to the direction the wave travels
Longitudinal Wave: Particles vibrate parallel to the direction the wave travels ex. sound wave Direction of travel Particles vibrate parallel to the direction of travel

Parts of a Longitudinal Wave:
Compression- point where the particles are closest together Rarefaction- point where the particles are furthest apart Rarefaction Compression

Intro Questions What do all waves transfer? What don’t waves transfer?
What starts a wave? Pick between the following choices and answer this correctly: 4. Sound is a (mechanical or electromagnetic) (transverse or longitudinal) wave.

Section 3: Relationship between Wavelength, Frequency and Wave Speed

Mechanical wave velocity
The velocity of the wave depends on the material it is traveling through. For a mechanical wave, which needs a medium, the more elastic the medium the faster the wave. Slower  Fastest Gas  liquid  solid

Electromagnetic Wave Velocity
The velocity of the wave depends on the material it is traveling through. For a electromagnetic wave, which can travel without a medium like in space, the more elastic the medium gets in the way and slows down the wave. Slower  Fastest No medium (space)  gas  liquid  solid

velocity ( v ): speed of the wave.
unit: m/s (meter/second) frequency ( f ): vibrations per second of the wave unit: Hz (hertz) wavelength ( ג ): length of one wave pulse unit: m (meter)

Lets revisit our old equation
What is the velocity of an object that moves 25 meters in 3 seconds?

Lets revisit our old equation
What is the velocity of an object that moves 25 meters in 3 seconds?

Now lets look at the new equation you can use as well.
old V= ___ d t Example what is the velocity of a wave that has a frequency of 3Hz and a wavelength of 5m?

Now lets look at the new equation you can use as well
old V= ___ d t

Now lets look at the new equation you can use as well
old V= ___ d t

Now lets look at the new equation you can use as well
old V= ___ d t

Now lets look at the new equation you can use as well
old V= ___ d t

Relationship between frequency and wavelength when wave velocity is the same.
Wavelength and frequency are inversely related As frequency goes up the wavelength gets shorter (assuming no change in velocity) Click for animation

Period (T) vs. Frequency (f)
Period (T) – seconds for one cycle (unit s) Frequency (f) – cycles for one second (unit Hz) If you know one you can solve for the other

Example 1 Wave Math The frequency of a wave is 560 Hz. What is its period?

The frequency of a wave is 560 Hz. What is its period?

Example 2 Wave Math A girl floats in the ocean and watches 12 wave crests pass her in 46 s. Calculate the wave: a) frequency b) period

A girl floats in the ocean and watches 12 wave crests pass her in 46 s
A girl floats in the ocean and watches 12 wave crests pass her in 46 s. Calculate the wave: a) frequency b) period

Example 3 Wave Math The period of a wave is 0.044s. How many cycles will the energy source make in 22s? cycles second

The period of a wave is 0.044s. How many cycles will the energy source make in 22s?

Example 4 Wave Math A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m. A. What is the wavelength? B. What is the amplitude? 0.33m 0.24m

Example 4 Wave Math A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m. A. What is the wavelength? B. What is the amplitude? 0.33m 0.66m

Example 4 Wave Math A distance of 0.33 m separates a wave crest from the adjacent trough, and the vertical distance from the top of a crest to the bottom of a trough is 0.24m. A. What is the wavelength? B. What is the amplitude? 0.12m 0.24m

Example 5 Wave Math What is the speed of a 256 Hz sound with a wavelength of 1.35 m?

Example 5 Wave Math What is the speed of a 256 Hz sound with a wavelength of 1.35 m?

Example 6 Wave Math You dip your finger into a pan of water 14 times in 11s, producing wave crests separated by 0.16 m. A. What is the frequency? B. What is the period? C. What is the velocity?

Example 6 Wave Math You dip your finger into a pan of water 14 times in 11s, producing wave crests separated by 0.16 m. A. what is the frequency B. What is the period C. Velocity

Section 4: The Pendulum

Movement from a to c and back to a is one complete cycle or vibration
Pendulum- a weight on a string that moves in simple harmonic motion (swings back and forth). Movement from a to c and back to a is one complete cycle or vibration This is the equilibrium position. decelerating accelerating

Simple harmonic motion- vibration about an equilibrium position
Constant back and forth motion over the same path. 15º is the maximum angle for a pendulum to have simple harmonic motion where our equations work

Masses do not effect the period in simple harmonic motion.
What effects the period: L – length of the string g – acceleration due to gravity

Example 7 A tall tree sways back and forth in the breeze with a frequency of 2Hz. What is the period of this tree?

Example 7 A tall tree sways back and forth in the breeze with a frequency of 2Hz. What is the period of this tree?

Example 8 Hypnotist Paulbar the great swings his watch from a 0.20 m chain in front of a subjects eyes. What is the period of swing of the watch.

Example 8 Hypnotist Paulbar the great swings his watch from a 0.20 m chain in front of a subjects eyes. What is the period of swing of the watch.

Example 9 A spider swings slightly in the breeze from a silk thread that is 0.09 m in length. What is the period of the simple harmonic motion?

Example 9 A spider swings slightly in the breeze from a silk thread that is 0.09 m in length. What is the period of the simple harmonic motion?

Example 10 If a pendulum is shortened, does the period increase or decrease? What about its frequency?

Example 10 If a pendulum is shortened, does the period increase or decrease? What about its frequency? Period decreases Frequency increases

Finish section 4 of the worksheets and turn in your packet today when you are done.
Work on something else quietly while you wait for everyone to complete their work

Section 5: Wave Interactions
Reflection Refraction Diffraction Interference

Reflection: The turning back of a wave at the boundary of a new medium (bouncing back) Ex: light off a mirror, or sound echo Incident wave- incoming

Waves reflected off a fixed boundary are inverted.
A fixed boundary is one not allowed to move

Waves reflected off a flexible boundary are upright.
A flexible boundary is allowed to move

Angle of reflection of a wave equals angle of incidence θr = θi
Law of Reflection: Angle of reflection of a wave equals angle of incidence θr = θi Normal line – line perpendicular to surface being reflected off of. θi Normal line θr

Example 11 Draw the reflected wave, labeling angles of incidence, reflection, and the normal line 35º

Wave front: Portion of a medium’s surface in which particles are in phase Particles in phase are in the same stage of their vibration.

Refraction: the bending of a wave path as it enters a new medium obliquely (indirectly) caused by difference in speed of the new medium fast to slow – bends toward the normal line slow to fast – bends away from normal

Refraction Light travels slower in water

Example 13 Draw the refracted wave, labeling the normal line, angle of incidence, and angle of refraction. Normal line θi Slow θr Fast

Diffraction: Spreading of waves around edges or through an opening of a boundary Is greatest when size of opening is smaller than wavelength

Principle of Superposition:
Displacement of a medium by two or more waves is the algebraic sum of the displacements of the waves alone

Interference: Result of the superposition of two or more waves constructive- (crest meets crest or trough meets trough) amplitudes add destructive – (crest meets trough) amplitudes subtract Only temporary as paths cross

Constructive interference
Only temporary as paths cross

Destructive interference
Only temporary as paths cross

Constructive and destructive interference in two sine waves

Example 14 (finish off the drawings)
Before During After Constructive interference Destructive interference

Wave Fronts Interfering
Nodal line Lines of destructive interference Antinodal line Lines of constructive interference

Standing wave: created by waves with same frequency, wavelength, and amplitude traveling in opposite directions and interfering. consists of nodes (o amplitude) and antinodes (max amplitude) produced by certain frequencies

Standing Waves Being Produced
Antinode Node

Section 6: Sound

Sound waves are produced by a vibrating object
Sound waves are longitudinal mechanical waves.

Sound Frequency: Determines pitch
20 – 20,000 Hz are audible to an average person Less than 20 Hz are infrasonic Greater than 20,000 Hz are ultrasonic Click for Frequency Modulator

Echolocation and Sonar
Sonar is simply making use of an echo. An echo is used to locate an object. When an animal or machine makes a noise, it sends sound waves into the environment around it. Those waves bounce off nearby objects, and some of them reflect back to the object that made the noise. Whales, Dolphins, Bats, and many more organisms use sound for locating prey and predators

Less than 20 Hz- Infrasonic

Generally between phases vsolids > vliquids > vgases
Sound Velocity Largely depends on medium elasticity Solids>liquids>gasses Then depends on temperature Faster at higher temperatures Air (at 0ºC) v = 331 m/s and +/- 0.6 m/s per ºC Generally between phases vsolids > vliquids > vgases

Sound Velocity Equations
v = Tc v = d/t v = fλ

Interesting sound facts
Sound travels 15 times faster in the steel from a railroad track. Sound travels 4 times faster in water At sea level, the speed of sound is 340 m/s or 760 mi/hr. This is called mach 1.

The speed of sound will be the same for all frequencies under the same conditions.
Wavelength and frequency are inversely related As frequency goes up the wavelength gets shorter 79

Example 15 What is the speed of sound at room temperature (22ºC)

What is the speed of sound at room temperature (22ºC)

Example 16 How many seconds will it take to hear an echo if you yell toward a mountain 110 m away on a day when air temperature is -6.0 ºC?

How many seconds will it take to hear an echo if you yell toward a mountain 110 m away on a day when air temperature is -6.0 ºC?

Example 17 If sound travels at 340 m/s, how many seconds will it take thunder to travel 1609m?

Example 17 If sound travels at 340 m/s, how many seconds will it take thunder to travel 1609m?

Example 18 A sonar echo takes 3.1s to go to a submarine and back to the ship. If sound travels at 1400m/s in water, how far away is the submarine?

Example 18 A sonar echo takes 3.1s to go to a submarine and back to the ship. If sound travels at 1400m/s in water, how far away is the submarine?

Example 19 On a day when air temperature is 11ºC, you use a whistle to call your dog. If the wavelength of the sound produced is 0.015m, what is the frequency? Could you hear the whistle?

Example 19 On a day when air temperature is 11ºC, you use a whistle to call your dog. If the wavelength of the sound produced is 0.015m, what is the frequency? Could you hear the whistle?

Section 7: The Doppler Effect

Doppler Effect Change in pitch caused by relative motion of source and observer Pitch increases as sound and observer approach (and vice versa)

Doppler Effect Problems
Frequency rises when its coming closer and lowers when moving away.

Example 20 Sitting on a beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of airplanes leaving Kennedy Airport. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies towards her at a speed of m/s? (use 340 m/s as the speed of sound)

Example 20 Sitting on a beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of airplanes leaving Kennedy Airport. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies towards her at a speed of m/s? (use 340 m/s as the speed of sound)

Example 21 Sitting on a beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of airplanes leaving Kennedy Airport. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies away from her at a speed of m/s? (use 340 m/s as the speed of sound)

Example 21 Sitting on a beach at Coney Island one afternoon, Sunny finds herself beneath the flight path of airplanes leaving Kennedy Airport. What frequency will Sunny hear as a jet, whose engines emit sound at a frequency of 1000 Hz, flies away from her at a speed of m/s? (use 340 m/s as the speed of sound)

Example 22 A sparrow chases a crow with a speed of 4.0 m/s, while chirping at a frequency of Hz. What frequency of sound does the crow hear as he flies away from the sparrow at a speed of 3.0 m/s? (use 340 m/s as the speed of sound)

Example 22 A sparrow chases a crow with a speed of 4.0 m/s, while chirping at a frequency of Hz. What frequency of sound does the crow hear as he flies away from the sparrow at a speed of 3.0 m/s? (use 340 m/s as the speed of sound)

Intro You are chasing after your parent’s car because you forgot your lunch in it. You are running at a swift 4.0 m/s and your parent is going 12 m/s. It is a cold 5.0° C today and your voice is producing a frequency of 460 Hz. Your parent’s car is squealing a bit and producing a frequency of 760 Hz. What frequency would your parent hear you at if he/she could? What frequency do you hear your parent’s car at?

You are chasing after your parent’s car because you forgot your lunch in it. You are running at a swift 4.0 m/s and your parent is going 12 m/s. It is a cold 5.0° C today and your voice is producing a frequency of 460 Hz. Your parent’s car is squealing a bit and producing a frequency of 760 Hz. What frequency would your parent hear you at if he/she could?

You are chasing after your parent’s car because you forgot your lunch in it. You are running at a swift 4.0 m/s and your parent is going 12 m/s. It is a cold 5.0° C today and your voice is producing a frequency of 460 Hz. Your parent’s car is squealing a bit and producing a frequency of 760 Hz. 2. What frequency do you hear your parent’s car at?

CW/HW Section 7 of Worksheet Packet

Section 8: Intensity and Perceived Sound

The property of sound waves associated with loudness is amplitude
The property associated with pitch is frequency

Section 9: Resonance and Music

Resonance in Music Forced Vibration- The vibration of an object that is made to vibrate by another vibrating object. Sympathetic vibrations- secondary vibrations caused by forced vibration of a first object. Sounding board- part of an instrument forced into vibration to amplify sound

Example of creating forced vibrations to make a sound louder
Sounding board of a musical instrument. Example: guitar makes a strings vibrations resonate

Resonance: Also called sympathetic vibrations
Dramatic increase in the amplitude of a wave when the frequency of an applied force matches the natural frequency of the object.

Resonance can be dangerous
Wind caused the Tacoma Narrows suspension bridge to vibrate at its natural frequency. The amplitude of the vibrations caused too much strain on the bridge until it collapsed.

Difference between music and noise
Noise- a random mixture of a large number of sound frequencies Music- Sound frequency or mixture of frequencies with a pattern

Percussion Instrument:
Musical sound produced by striking the object Frequency depends on the mass of the object. To raise the pitch- decrease the mass of the object. Ex- drums, xylophone, bells

Stringed Instrument Musical sound produced by plucking or blowing strings Frequency depends on four factors To raise pitch 1. decrease diameter of string 2. increase tension 3 decrease length 4. decrease density of string material Examples: guitar, violin

Wind Instrument Musical sound produced by vibrating air column
Frequency depends mainly on length of air column To raise pitch- decrease the size of the air column Examples- oboe, flute

Standing Waves are formed in the instrument due to vibrations
When the natural frequency is hit the sound amplifies

Open Ended Wind Column Instrument
Must be nodes at both ends

Closed Ended Wind Column Instrument
There is an antinode at the closed end. Count standing waves by including the return trip.

Acoustics- field of study related to sound
Acoustic designers try to maximize the quality of sound reaching the audience Control the size, shape, and material used They try and control the reflection

Two types of reflection with sound
Reverberation- If a reflected sound wave reaches the ear within 0.1 seconds of the initial sound, then it seems to the person that the sound is prolonged. Echoes- A perceived second sound that arrives after the first has died out. Echoes occur when a reflected sound wave reaches the ear more than 0.1 seconds after the original sound wave was heard.

Interference causes beats
Beats occur due to constructive and destructive interference between sounds with close but not exact frequencies.

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