1. Sound Learning Objectives:
Recall that sound waves are caused by vibrations.
Recall that sound waves are longitudinal waves.
Describe how wavelength, frequency, and amplitude of a wave affects how it sounds.
Draw sound waves for different sounds.

2. Sounds are caused by vibrations
What is vibrating?

3. We can cause vibration by…
Making a column of air vibrate
Plucking a string
Hitting an object

4. Sounds waves are longitudinal waves
How do vibrations form longitudinal waves?

5. The air particles return to their original position when the object vibrates the other way.
This causes an area of rarefaction.
The vibrating object pushes against air particles.
These particle bump into other air particles and cause an area of compression to form.

6. This causes pressure changes

8. Sound is caused by vibrations

9. What mediums can sound travel through?
Speed of sound…
Through air 300 m/s
Through water m/s
Through iron m/s
BUT!
Sound can NOT travel through a vacuum (empty space) because there are no particles to vibrate.
Bell Jar Demo
How do astronauts talk?

10. Check for understanding:
09/11/2018
Check for understanding:
Sound waves are mechanical waves. This means that they need a medium (e.g., air) to travel through.
Sound waves are longitudinal waves. This is because the direction of the vibrations is parallel to the direction the wave travels.
mechanical
vibrations
parallel
longitudinal
medium

11. 09/11/2018 Solid Liquid Gas The particles are very close together
The particles are close together
The particles are very far apart
Particles often bump into each other
Particles bump into each other less often
Particles do not often bump into each other
It is easy for vibrations to be passed on
It is less easy for vibrations to be passed on
It is difficult for vibrations to be passed on
Sound travels faster than in liquids and gases
Sound travels faster than in gases
Sound travels slowest in gases
How close together are the particles?
How often do they bump into each other?
How easy is it for the vibrations to be passed on?
How fast does sound travel in this medium?

12. What makes sounds different?
The amplitude, frequency and wavelength will affect how a wave sounds.

13. When the frequency of sound waves change, we hear different pitches.
09/11/2018
When the frequency of sound waves change, we hear different pitches.
High pitch
(high frequency)
Low pitch
(low frequency)

14. The amplitude will affect the loudness of the sound.
Quiet Sound
Loud
Sound

15. Compare the sounds for the following waves.B E
Same frequencies / wavlengths: D & F, A & E.
Same amplitudes: B & E, C & F C F

16. How does the ear work?
1) Sound waves are “funnelled” into the ear by the pinna
5) The electrical signals are then sent to the brain
4) These vibrations are turned into electrical signals in the cochlea
3) These vibrations make the ear bones vibrate
2) These vibrations make the ear drum vibrate

17. The human ear can hear frequencies that range from 20 Hz to 20,000 Hz.
09/11/2018
The human ear can hear frequencies that range from 20 Hz to 20,000 Hz.

18. 09/11/2018
How loud does a sound have to be before we can hear it? What happens if it is too loud?

19. The loudness of a sound is measured in decibels (dB).
09/11/2018
How loud does a sound have to be before we can hear it? What happens if it is too loud?
The loudness of a sound is measured in decibels (dB).
The quietest sound we can hear is 0 dB. This is called the threshold of hearing.
Sound starts to become painful at 134 dB.
The eardrum breaks at 185 dB.

20. The loudness of a sound is measured in decibels (dB).
09/11/2018
How loud does a sound have to be before we can hear it? What happens if it is too loud?
The loudness of a sound is measured in decibels (dB).
The quietest sound we can hear is 0 dB. This is called the threshold of hearing.
Sound starts to become painful at 134 dB.
The eardrum breaks at 185 dB.

21. The loudness of a sound is measured in decibels (dB).
09/11/2018
How loud does a sound have to be before we can hear it? What happens if it is too loud?
The loudness of a sound is measured in decibels (dB).
The quietest sound we can hear is 0 dB. This is called the threshold of hearing.
Sound starts to become painful at 134 dB.
The eardrum breaks at 185 dB.

22. The loudness of a sound is measured in decibels (dB).
09/11/2018
How loud does a sound have to be before we can hear it? What happens if it is too loud?
The loudness of a sound is measured in decibels (dB).
The quietest sound we can hear is 0 dB. This is called the threshold of hearing.
Sound starts to become painful at 134 dB.
The eardrum breaks at 185 dB.

23. The loudness of a sound is measured in decibels (dB).
09/11/2018
How loud does a sound have to be before we can hear it? What happens if it is too loud?
The loudness of a sound is measured in decibels (dB).
The quietest sound we can hear is 0 dB. This is called the threshold of hearing.
Sound starts to become painful at 134 dB.
The eardrum breaks at 185 dB.