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.

http://www.youtube.com/watch?v=s9GBf8y0lY0&feature=PlayList&p=1E3D8BA115599599&playnext=1&playnext_from=PL&index=29

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.