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Chapter 15 Chapter 16Waves and Sound
•A repeating disturbance /movement that transfers energy through matter or space.
What is a wave?
Waves transfer energy not matter.
Waves exist if they have energy to carry. Vibration is transferred from particle to particle ……..
Types of waves: Waves are classified according to how they
move.
1) Mechanical waves
Require a medium to carry the energy.
***Waves such as light, x-rays, and other forms of radiation do not require a medium*** - not mechanical.
Types of Waves
A)Transverse Waves
Matter in the wave moves up and down at a right angle to the direction of the wave
What are the parts of a wave?Transverse wave
The crest is highest point
The trough is lowest point.
The rest position is called the node.
The wavelength is the distance from one point on the wave to the next corresponding adjacent point.
amplitude – height of wave
It is directly related to the amount of energy in a wave.
B) Longitudinal Waves
(Compression Waves)
Matter in the wave moves back and forth parallel to the direction of the wave.
Ex: Sound
Parts of a Compressional or Longitudinal wave
The area squeezed together is the compression.
The area spread out is the rarefaction.
Wavelength : The distance from the center of one compression to the center of the next compression.
Amplitude = Density Which Spring has more energy?
Longitudinal or Transverse?
What is wavelength?
Wavelength measures distance.
Use distance units
What is wave frequency?
Frequency measures the number of waves that pass through a point in one second.
Unit for frequency - # waves per second (Hertz - Hz). One Hz = One wave per second.
• 1 cycle = 1 full wave to repeat
itself
3 3 11 22 44 55 66 77 88 99 1010 1111 1212
Time in seconds Time in seconds
3 cycles3 cycles
Wavelength and frequency are inversely related.
What is the Frequency??
12 Hz
6 Hz
A wave moving through a medium travels at a certain speed. This is Wave Speed.
How is Wave Speed calculated?
Wavelength is represented by Greek letter lambda (λ)
and frequency is represented by (f)
A wave has a wavelength of 15 cm and has a frequency of 10 waves/second. What is the speed of the wave?
(λ) = 15 cm
f = 10 waves/second
V = ?
V = .15m x 10 hz = 1.5 m/s
The speed of a wave on a rope is 50cm/s and it’s wavelength is 10cm. What is it’s frequency?
V = 50cm/s
(λ) = 10 cm
f = ?
f = V / (λ) =5 Hz
Can you draw a wave?Can you draw a wave?
Slinky Lab-
• Teams of 3 – 1 timer, 2 wave makers• Read lab procedure before doing anything!!!! It can be tricky!!
• Complete data table as presented.
Section 15.3 – Interactions of Waves (5)
1) REFLECTION• When energy hits a surface through which
it can not pass – it “bounces”.• A sound wave reflection = “an Echo”
• Smooth hard surfaces reflect best.• Rough soft surfaces reflect poorly.• Energy can also be absorbed or
transmitted.
2) RefractionWhen a wave enters a new medium at an angle, one side bends before the other. One side changes speed before the other.
Like light, sound can be…
Reflected – sound reflections are called echoes.
“Sounds Bounce”
Refracted –why you might sound strange if you try talking underwater...
“Sounds Bend”
3) Diffraction : When an object causes a wave to change direction and bend around it.
4) Wave Interference:
When 2 waves collide “in phase”
When 2 waves collide “out of phase
Chapter 16 - What is Sound?
Sound (compressional wave) travels through the air through a series of compressions and rarefactions.
Sound can travel through different media.
We hear sound usually through air.
1) The denser the medium, the faster sound will travel. Why?
2)The higher the temperature, the faster sound travels. Why?
What is Sound Intensity?
Sound Intensity = Energy of the sound wave.
The greater the intensity the farther the sound will travel and the louder the sound will appear.
“Loudness” is human perception of sound intensity.
Unit for loudness is decibels.(dB)
Loudness in Decibels
Normal Conversation – 60Fire Alarm - ( No less than 70 – no greater than 120)Shot Gun Blast- 170
How is frequency related to pitch?
Pitch of a sound wave is directly related to frequency.
A high-pitched sound = high frequency
A low-pitched sound = low frequency
What is the Doppler Effect?
The Doppler Effect is the apparent change in frequency detected when the sound is moving relative to the person hearing the sound.
http://www.youtube.com/watch?v=gzUhw1rRJtc
Doppler Effect
Video-Excellent example of Doppler Effect with car horn (26 seconds
)
Speed of Sound Lab
• How fast does Sound travel?
• Effect of Temperature? Wind?
• Calculate speed of sound
http://www.youtube.com/watch?v=pjP7hmBfYdA
Period
Temp (o C)
Other Conditions(Wind, noise, etc..)
HumidityLevels
Average Class Speed
4 8 am
46 F
8 C
Lawn mowerBirdsNo wind
87% 277.68 m/s
2 10 am
54 F 16 C
Wind 5mphAirplanes, Lawn mowers, trucks
64% 229.53 m/s
5 12 pm
65 F
19 C
Wind 5 mphAirplane, lunch time kids
41% 227.91m/s
61 pm
68F20 C
Wind NW 9 mphAirplane, lawn mower, chain saw
30% 241.62 m/s
72 pm
72 F22C
Wind SSW 5 mph 32% 236.91 m/s
Human Range• 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 20 Hz - Infrasonic– Sounds above 20,000 HZ- Ultrasonic
Hearing problems
Our hearing range can be damaged by several things:
1)Too much ear wax!
2)Damage to the auditory nerve
3)Illness or infections
4)Old age (sort of like Mrs. Hyland)
Around 80% of deafness is due to damage to the cochlea cells.
Deafness is one of the most common disabilities.
UltrasonicSounds above 20,000 Hz .
Some animals can hear frequencies in this range - (humans cannot).
Ex: Sonar, Medical uses
Sonar – A system that uses the reflection of underwater sound waves to detect objects.
Can determine distance.
ECHOLOCATION:High Frequency sounds that are emitted by certain animals to locate prey.
Sound waves bounce off and return to the animal (echoes) allowing the hunter to pinpoint location of prey.
Clicking noisesClicking noises
Ultrasonic cries
http://www.youtube.com/watch?v=XUXh-http://www.youtube.com/watch?v=XUXh-X1iveUX1iveU
Infrasonic sounds
http://www.youtube.com/watch?v=pLBe8sOPO7Yhttp://www.youtube.com/watch?v=pLBe8sOPO7Y
http://wn.com/infrasonic#/videoshttp://wn.com/infrasonic#/videos
http://www.youtube.com/watch?http://www.youtube.com/watch?v=fwrbFj9r10Yv=fwrbFj9r10Y
http://www.youtube.com/watch?v=gzUhw1rRJtc
http://www.youtube.com/watch?v=WuaEFR3wGQEhttp://www.youtube.com/watch?v=WuaEFR3wGQE
Wave Reflection – Do Now
Acoustics of room design: You need some reflections to “liven” the room.
Too many reflections and the sound gets mushy.
Think about a concert hall or auditorium and come up with some different sound treatments used.
What are some examples?
Whale strandings –Why do they do it?
A change in the behavior of dolphins has biologists concerned that use of low frequency sonar could be disorientating whales and dolphins.
• Using what you know about sound waves and sonar, explain what is happening to the animals.