# Waves and Sound. Intro A. Pick up your notes and worksheet packets B. Write the following questions on a blank piece of paper (don’t answer yet) 1. What.

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Waves and Sound

Intro A. Pick up your notes and worksheet packets B. Write the following questions on a blank piece of paper (don’t answer yet) 1. What is the difference between a mechanical and electromagnetic wave? 2. What is the difference between a transverse and longitudinal wave? 3. What do all waves transfer? 4. What don’t waves transfer?

Section 1: Intro to Waves

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

Mechanical wave: –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 SOL= 3.0 x 10 8 m/s Through empty space Types Electromagnetic Waves

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

Damping: A decrease in the amplitude of a wave Caused by energy loss or the spreading out of the wave over a larger area.

Wave pulse is a single wave disturbance Wave train (continuous wave) - is a series of pulses at intervals

Section 2: Types of Mechanical Waves Transverse Longitudinal

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

Parts of a transverse wave Crest Trough Equilibrium Position Wavelength (ג) amplitude

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

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 Compression Rarefaction

Intro Questions 1.What do all waves transfer? 2.What don’t waves transfer? 3.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

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? V= ___ dtdt

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

Now lets look at the new equation you can use as well. V= ___ dtdt oldnew 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 V= ___ dtdt oldnew

Now lets look at the new equation you can use as well V= ___ dtdt oldnew

Now lets look at the new equation you can use as well V= ___ dtdt oldnew

Now lets look at the new equation you can use as well V= ___ dtdt oldnew

Relationship between frequency and wavelength. 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?

Example 2 Wave Math A girl floats in the ocean and watches 12 wave crests pass her in 46 s. Calculate the wave: a) frequencyb) 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? 0.24m 0.12m

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

Assignment to work on: CP Worksheet Packet Section 3 Honors Worksheet Packet Section 3 Book Problems 4,5,6 pg 486-487

Pendulum Lab day: Your into is to read over your lab; I will ask you if there are any questions soon Equilibrium Position Amplitude (A) Length (L)

Pendulum Lab day One complete cycle

Intro after pendulum lab All labs are due today: Turn them in on my desk 1.Your pendulum makes 5 complete cycles in 10 seconds. a.What is the pendulums frequency? b.What is the pendulums period? 2.What is the definition of frequency (can be in equation form) 3.When you increase the length of the pendulum string, what happens to frequency?

Section 4: The Pendulum

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 accelerating decelerating This is the equilibrium position.

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?

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 8

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 9

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? Example 10 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 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

Law of Reflection: Angle of reflection of a wave equals angle of incidence θ r = θ i Normal line – line perpendicular to surface being reflected off of. θrθr θiθi Normal line

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.

Which two of these particles would be in phase? Example 12

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

Normal Line θiθi θrθr slow Fast medium

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

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

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) BeforeDuringAfter Constructive interference Destructive interference

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

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 NodeAntinode

Show what you know 1. Refraction happens when waves – a)Turn back at a boundary b)Enter a new medium at an angle. c)Go through an opening. d)Are superpositioned.

2. This diagram shows which wave interaction? a)Reflection b)Refraction c)Diffraction d)Interference

3. Constructive interference occurs when- a)Crest meets crest b)Trough meets trough c)Amplitudes add up d)All of these

4. A line along which the medium does not vibrate is called a a)Nodal line b)Antinodal line c)Construction

5. Standing waves are produced by waves of equal ________ traveling in opposite directions. a)Wavelength b)Frequency c)Amplitude d)All of the above

Intro Questions 1.An echo bouncing off a nearby wall tends to ________________ back toward the source. 2.A pendulum requires 3 seconds to make one back and forth motion. Calculate the pendulum’s frequency? 3. Steam is rising from a cup of hot tea. What type of thermal energy transfer is occurring? (conduction, convection, or radiation) 4. What type of interference would occur when these waves meet? 5. A water wave has a speed of 5m/s and the distance between each crest is 2.0m. What is the frequency of the water wave?

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

Uses of ultrasonic waves

More than 20,000 Hz- Ultrasonic waves

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- Subsonic or Infrasonic Sound

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 v solids > v liquids > v gases

Sound Velocity Equations v = 331 + 0.6 T c 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

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

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

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 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?

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?

Intro 1. A 25,000Hz dog whistle can be heard by a dog but not by humans because the frequency is in the ______________ range. 2. An elephant can hear below 20 Hz. This is the _________ range. 3. The range we can hear is between _____ and _______ and we call this range ______________. 4. Which of the following will sound travel fastest in? a) a swimming pool b) a steel bridge c) a vacuum d) warm air 5. Sound wave A has twice the frequency of sound wave B. That means that sound wave A must _______________ a) travel faster than sound wave B b) have a shorter wavelength than sound wave B c) have a lower pitch that sound wave B d) be louder than sound wave B

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 Example http://www.animations.physics.unsw.edu.a u/jw/doppler.htm#examplehttp://www.animations.physics.unsw.edu.a u/jw/doppler.htm#example

Examples/Uses Doppler radar: detects storm fronts and their approach speed.

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 100.0 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 100.0 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 100.0 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 100.0 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 850.0 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 850.0 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. 1.What frequency would your parent hear you at if he/she could? 2.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. 1.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?

Section 8: Intensity and Perceived Sound

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

Sound Intensity is the rate of transferring energy through an area

The Decibel Scale Threshold of hearing (I o )- –the minimum intensity sound that can be heard at certain frequencies I o = 1.0 x 10 -12 ß = 0 dB at the threshold of hearing

More on the Decibel Scale The decibel scale relates sound intensity to human hearing –An intensity of 0 dB is when there is enough energy for an average human to detect the sound –1-dB in intensity level is the smallest change in loudness that an average listener can detect –If the relative intensity level increases by 10 dB, the new sound seems approximately twice as loud as the original sound.

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

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. Two types of reflection with sound

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

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