1. Presented by Kesler Science
Sound Waves
Created by Kesler Science – More 5E lessons at KeslerScience.com
Presented by Kesler Science

2. Essential Questions: What is sound? How do sound waves travel?
How do physical properties of a medium affect the speed of sound waves?
What properties of waves affect what we hear?
What is the Doppler effect?

3. Sound Waves
Sound
Vibrations that travel through the air or other media
When these vibrations reach the air near your ears you hear the sound.

4. Quick Action – Sound Waves
Think about this riddle.
If a tree falls in a forest and no one is there to hear it, does the falling tree make a sound?
Discuss this with a partner.
Must you hear a vibration for it to be sound?
Is the energy produced by the vibration a sound if no one hears it?
Write your own definition for sound.

5. How Sound Travels Sound Waves
Sound waves carry energy through a medium (solid, liquid or gas) without the particles of the medium traveling along.
Sound travels as a longitudinal wave.

6. How Sounds are Made Sound Waves
Longitudinal waves are generated when a source of energy forces the matter in a medium to vibrate.
This back-and-forth motion pushes air particles together, generating a compression, or moves the particles apart, generating a rarefaction.
Compression
Rarefaction

7. Quick Action – Sound Waves
Together with a partner make a list of things that you use daily that make sounds.
Choose one of these objects and try to figure out how it makes vibrations.
Here is an example:
When you strike a drum you cause the drumhead to
push inward. The drumhead then rebounds in the
opposite direction. Each movement creates
compressions and rarefactions.
Be prepared to share with the class.

8. Medium Sound Waves Sound waves must have a medium to travel through.
Gas – air is the most common
Liquid
Solid
In outer space there are no molecules to compress or rarefy, so sound does not travel through outer space.

9. Speed of Sound Sound Waves
Depends on the physical properties of the medium it travels through.
Elasticity
Density
Temperature
At room temperature, sound travels through air at about 342m/s.
Speed of Sound
Medium
Speed(m/s)
Gases
Air (0o C)
330
Air (20oC)
342
Liquids
Fresh water
1,490
Salt water
1,530
Solids (25oC)
Hard wood
4,000
Glass
4,540
Steel
5,200

10. Physical Properties of Media
Sound Waves
Physical Properties of Media
Elasticity – the ability of a material to bounce back after being disturbed
Solid materials are usually more elastic than liquids or gases.
Particles of a solid do not move very far, so they bounce back and forth quickly as the vibration travels through the object, which allows waves to move faster.
Liquid
Gas
Distance traveled in 1 sec.
Solid

11. Quick Action – Sound Waves
Write About
Look back at the previous slide.
Compare the speed of waves in solids, liquids and gases.
Explain in your own words how elasticity affects the speed of sound waves.
2 min. … go!

12. Physical Properties of Media (cont.)
Sound Waves
Physical Properties of Media (cont.)
Density – how much matter there is in a given amount of space
The speed of sound depends on how close together the particles of the substance are in the medium.
Speed of Sound
Medium
Speed(m/s)
Density
Gas
Least dense
Air
342
Liquid
Fresh water
1,490
Solid
Steel
5,200
Most dense
This can become confusing to middle school students as particle size in relation to density can slow sound waves. So just talk about how sound waves move faster in solids and slower in gases.

13. Physical Properties of Media (cont.)
Sound Waves
Physical Properties of Media (cont.)
Temperature - degree or intensity of heat present in a substance or object
In a given media (solid, liquid, gas), sound travels more slowly at lower temperatures.
Air Temperature (oC)
Speed
(m/s)
-20
318
-10
324
330 10
336 20
342 30
348

14. Properties of Sound Waves
Intensity
Loudness
Frequency
Pitch

15. Properties of Sound Waves
Intensity – the amount of energy the wave carries per second through a unit of area
Amplitude increases with increased energy
Measured in watts per square meter (W/m2)

16. Properties of Sound Waves (cont.)
Loudness – describes what you actually hear.
Though not the same as loudness, the greater the intensity of a sound wave, the louder it is.
Measured in decibels (dB)
Maximum safe level is 85 dB

17. Properties of Sound Waves (cont.)
Frequency – the number of vibrations that occur per second
Wavelength changes with frequency
Measured in Hertz (Hz)
50Hz = 50 vibrations per second
Which wave has the greatest frequency?

18. Properties of Sound Waves (cont.)
Pitch – a description of how high or low the sound seems to a person
High frequency = high pitch
Low frequency = low pitch
Example: a young girl might have a squeaky (high pitched) voice, an older man might have a deep (low pitched) voice

19. Quick Action – Sound Waves
Write About
Get with a partner and discuss the physical properties of sound waves: intensity, loudness, frequency and pitch.
Write a phrase or sentence describing how frequency and pitch are related.
Write another phrase or sentence describing how intensity and loudness are related.

20. Doppler Effect Sound Waves
The apparent change in frequency as a wave source moves in relation to the listener
Sounds moving toward a person – Waves are at a higher frequency, so pitch appears to increase (high)
Sound moving away from a person – Waves are at a lower frequency, so pitch appears to decrease (low)
Chris, can you put this video clip on this slide?

21. Check for Understanding
Can you…
define sound?
explain how sound waves travel?
describe the physical properties of a medium and explain its effect on the wave‘s speed?
compare the properties of waves that affect what we hear?
demonstrate the Doppler effect?
Clear up any confusion and answer questions.

22. Ear
Broken into three sections: outer, middle, and inner

24. Outer Ear Only two structures Actual “ear” that we see is the pinna
Opens to a tube called auditory cannal
Both are designed to collect logitudinal compression and rarefaction waves

25. Middle Ear Contains three bones (smallest in the body)
All three - malleus, incus, and stapes (hammer, anvil, and stirrup) transmit the vibrational waves to the oval window, a membrane connected to the inner ear
Also in middle is a opening to the pharynx called the Eustachian tube
Regulates pressure affecting tympanic membrane

26. Inner Ear Actual center where sound waves are processed
Has fluid filled chambers called semicircular canals, responsible for spatial orientation
The cochlea is the hearing centre
Connected to auditory nerve, which relays info to auditory complex in cerebrum