1. Interactions of Sound Waves
Crest
Trough
Unit 2 Lesson 2
Interactions of Sound Waves

2. Some Like It Hot What affects the speed of sound?
Unit 2 Lesson 2 Interactions of Sound Waves
Some Like It Hot
What affects the speed of sound?
There are two main factors that affect the speed of sound: the type of medium the sound travels through, and the temperature of the medium.
If we know these factors, we can predict the speed of sound.

3. What affects the speed of sound?
Unit 2 Lesson 2 Interactions of Sound Waves
What affects the speed of sound?
The speed of sound depends on the type of matter, or medium, through which sound travels.
The state of matter also affects sound waves.
Sound travels fastest through solids, slower through liquids, and slowest through gases.
The more packed together the particles are, the faster the wave will travel.

4. What affects the speed of sound?
Unit 2 Lesson 2 Interactions of Sound Waves
What affects the speed of sound?
The speed of sound depends on the temperature of a medium.
Sound travels faster at higher temperatures than at lower ones.
Particles in a material move more quickly at higher temperatures and transfer energy faster.
Sound moves faster at higher temperatures and slower at cooler temperatures.

5. Hello? Hello? Hello? How do sound and matter interact?
Unit 2 Lesson 2 Interactions of Sound Waves
Hello? Hello? Hello?
How do sound and matter interact?
Sound waves do not travel easily through all matter.
Sound may bounce away from some surfaces. Sound may be absorbed by other sources or transmitted through a barrier
Reflection is the bouncing back of a wave when it hits a barrier. Sound waves reflect best off smooth, hard surfaces.

6. How do sound and matter interact?
Unit 2 Lesson 2 Interactions of Sound Waves
How do sound and matter interact?
Some matter absorbs sound waves better than other matter.
A rough wall will absorb sound better than a smooth wall will.
Soft materials, such as rugs and drapes, will absorb sound better than hard surfaces will.

7. How do sound and matter interact?
Unit 2 Lesson 2 Interactions of Sound Waves
How do sound and matter interact?
How will sound waves travel differently in each room?

8. What is an echo? An echo is a reflected sound wave.
Unit 2 Lesson 2 Interactions of Sound Waves
What is an echo?
An echo is a reflected sound wave.
The strength of the echo depends on the reflecting surface.
Echoes can be reduced using soft materials that absorb the sound waves.
Echoes can also be reduced using rough surfaces that scatter the sound waves.

9. Unit 2 Lesson 2 Interactions of Sound Waves
What is an echo?
Some animals—such as dolphins, bats, and beluga whales—use echoes to hunt for food and find objects in their path.
The use of reflected sound to find objects is called echolocation.
People use a type of echolocation called sonar (sound navigation and ranging).
Sonar is electronic echolocation used to locate objects underwater.

10. What is an echo? How do bats use echolocation?
Unit 2 Lesson 2 Interactions of Sound Waves
What is an echo?
How do bats use echolocation?

11. Boom! How do sound waves interact with each other?
Unit 2 Lesson 2 Interactions of Sound Waves
Boom!
How do sound waves interact with each other?
Interference happens when two or more waves overlap and combine to form one wave.
In music, beats happen when two sound waves with nearly equal frequencies interfere.
Since the frequencies are not quite equal, they form a repeating pattern of constructive and destructive interference that sounds loud and soft.

12. How do sound waves interact with each other?
Unit 2 Lesson 2 Interactions of Sound Waves
How do sound waves interact with each other?
When constructive interference occurs, waves overlap and combine to form a wave with a larger amplitude, or height.
Constructive waves can cause
very loud sounds, such as
sonic booms.

13. How do sound waves interact with each other?
Unit 2 Lesson 2 Interactions of Sound Waves
How do sound waves interact with each other?
In destructive interference, waves combine to form a wave with a smaller amplitude.
The sound will be softer because
the amplitude is decreased.
Noise cancelling headphones use
destructive interference.

14. How does interference cause sonic booms?
Unit 2 Lesson 2 Interactions of Sound Waves
How does interference cause sonic booms?
Jet planes moving faster than the speed of sound can produce a very loud sound called a sonic boom.
This sound can rattle and even break windows.
When a jet travels very fast, it catches up to its own sound.

15. How does interference cause sonic booms?
Unit 2 Lesson 2 Interactions of Sound Waves
How does interference cause sonic booms?
The waves pile up as a result of constructive interference.
This interference forms a high pressure area called a sound barrier.
If a jet travels fast enough, it breaks through the barrier and forms a single shock wave that is heard as a loud boom.
The jet must travel at supersonic speeds, or speeds faster than the speed of sound.

16. How does interference cause sonic booms?
Unit 2 Lesson 2 Interactions of Sound Waves
How does interference cause sonic booms?
How does this jet create a sonic boom?

17. Good Vibrations What is resonance?
Unit 2 Lesson 2 Interactions of Sound Waves
Good Vibrations
What is resonance?
Resonance happens when a sound wave matches the natural frequency of an object and causes the object to vibrate.
If a sound wave in the room forces air in a seashell to vibrate at its natural frequency, resonance occurs.
This resonance results in a big vibration that sounds like the ocean when you hear it.

19. Where can resonance occur?
Unit 2 Lesson 2 Interactions of Sound Waves
Where can resonance occur?
All objects have a frequency, or set of frequencies, at which they vibrate.
These are called natural frequencies, or resonant frequencies.
Resonance will happen whenever an object vibrating at or near the natural frequency of a second object causes the second object to vibrate as well.

20. Where can resonance occur?
Unit 2 Lesson 2 Interactions of Sound Waves
Where can resonance occur?
Resonance is important for making music.
Vibrations make a sound that gets louder when it forms a standing wave inside the instrument.
A standing wave is a pattern of vibration that looks like the wave is standing still.
Resonance occurs when standing waves are formed.

21. Where can resonance occur?
Unit 2 Lesson 2 Interactions of Sound Waves
Where can resonance occur?
Resonance can even occur in buildings, towers, and bridges.
Simple activities such as marching can create resonance to cause a bridge to sway or collapse.
Engineers plan their designs to prevent resonance that could collapse a structure.
Overlapping plates cause friction to keep resonance from becoming destructive.

22. Unit 2 Lesson 3
Sound Technology

23. Hello Hello Hello How are echoes used?
Unit 2 Lesson 3 Sound Technology
Hello Hello Hello
How are echoes used?
Echolocation is the use of echoes to find food and other objects.
Animals produce ultrasound, which are sound waves that have frequencies greater than 20,000 Hz, for echolocation. The frequencies of these ultrasonic waves are too high for humans to hear.
The time it takes for ultrasound to bounce off an object and return to the animal tells the animal how far away the object is.

24. Unit 2 Lesson 3 Sound Technology
How are echoes used?
Though people cannot send out or hear ultrasound, people can still use echolocation in various technologies.
Sonar is a system that uses echoes to determine the locations of objects or to communicate.
Sonar is used to map out ocean floors, find fish, avoid icebergs, and help visually impaired people navigate on land.

25. How are echoes used? How is sonar used to map the ocean floor?
Unit 2 Lesson 3 Sound Technology
How are echoes used?
How is sonar used to map the ocean floor?

26. Unit 2 Lesson 3 Sound Technology
How are echoes used?
Ultrasound procedures use high-frequency sounds to produce images of the inside of a person’s body.
Ultrasound that has a frequency of 1 million to 10 million hertz can pass into a person’s body.
Ultrasounds do not harm human cells, like x-rays do.

27. Unit 2 Lesson 3 Sound Technology
How are echoes used?
The sound waves reflect when they meet internal organs.
The reflected waves create an image of whatever organ they bounce off of.
Ultrasounds are used to check how a fetus is growing in a mother’s body.

28. How do telephones transmit sound?
Unit 2 Lesson 3 Sound Technology
How do telephones transmit sound?
Sound waves lose energy over time.
Phones change sound waves into other types of signals that can be sent over long distances.
These signals are then changed back into sound waves that can be heard.

29. How do telephones transmit sound?
Unit 2 Lesson 3 Sound Technology
How do telephones transmit sound?
All telephones change sound into electrical signals.
Cordless phones change the electrical signal into radio waves that travel through air at the speed of light.
The base picks up the radio waves and changes them back into electrical signals that are sent through wires.
A computer sends these signals to the other phone, where they are changed back into sound waves.

30. Unit 2 Lesson 3 Sound Technology
Hello, Operator
People used to have to call telephone operators, who plugged wires into a switchboard to connect one phone to another.
The invention of the rotary dial made it possible for people to call a number directly, replacing telephone operators.
Cell phones use radio waves to send signals to phone towers. The towers transfer the signals to phone cables.

31. Groovy How is sound recorded and played back?
Unit 2 Lesson 3 Sound Technology
Groovy
How is sound recorded and played back?
Sound is recorded to preserve sound information, such as interviews and music.
Thomas Edison invented the phonograph, which could record and play back sound.
Information in sound was recorded in the grooves of records. Now it is stored on CDs or in computer files.

32. How is sound recorded and played back?
Unit 2 Lesson 3 Sound Technology
How is sound recorded and played back?
A compact disc, or CD, is made of hard plastic.
The information in sound waves is stored by pressing microscopic pits into the plastic.
Light from a laser reflects off the shiny surface as the CD rotates.
The detector changes the pattern into an electrical signal, which is then changed back into sound waves.

34. How is sound recorded and played back?
Unit 2 Lesson 3 Sound Technology
How is sound recorded and played back?
Sound is also recorded as a digital file in a computer.
Digital files, such as MP3 files, store large amounts of information.
More sound files can be stored in a computer or an MP3 player than on a CD.

35. How is sound recorded and played back?
Unit 2 Lesson 3 Sound Technology
How is sound recorded and played back?
First, the original sound gets changed into an electrical signal.
Then, it is stored as a digital file on a hard drive. The digital file is a series of 1s and 0s.
Software reads the files and produces electrical signals that are sent to speakers.
The speakers change the signal back into sound waves.