• A repeating disturbance /movement that transfers energy through matter or space.

Waves transfer energy not matter.
Waves exist if they have energy to carry.
Vibration is transferred from particle to particle ……..

Types of Waves
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.

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?

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.

3 cycles
1 2 3
4 5 6 7 8 9 10 11 12
Time in seconds

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?

• 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) Refraction
When 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 – 60
Fire 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=gzU hw1rRJtc

)
VideoExcellent example of Doppler Effect with car horn (26 seconds

• How fast does
Sound travel?
• Effect of
Temperature?
Wind?
• Calculate speed of sound

Period Temp
(o C)
4
8 am
46 F
8 C
2
10 am
54 F
16 C
Other
Conditions
(Wind, noise, etc..)
Lawn mower
Birds
No wind
Wind 5mph
Airplanes, Lawn mowers, trucks
Humidity
Levels
87%
64%
5
12 pm
6
1 pm
65 F
19 C
Wind 5 mph
Airplane, lunch time kids
68F
20 C
Wind NW 9 mph
Airplane, lawn mower, chain saw
41%
30%
7
2 pm
72 F
22C
Wind SSW 5 mph
32%
Average
Class
Speed
277.68 m/s
229.53 m/s
227.91m/s
241.62 m/s
236.91 m/s

• 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 HZUltrasonic

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.

Sounds 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.

Clicking noises
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.
Ultrasonic cries http://www.youtube.com/watch?v=XUXh-
X1iveU

http://www.youtube.com/watch?v=pLBe8sOPO7Y http://wn.com/infrasonic#/videos http://www.youtube.com/watch?v=fwrbFj9r
10Y

http://www.youtube.com/watch?v=gzU hw1rRJtc http://www.youtube.com/watch?v=WuaEFR3wGQE

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?

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.