1. Sound
As we know, sound waves are formed when something vibrates. But how does the sound reach our ears?
Air molecules
2) The vibrations pass through air by making air molecules vibrate
3) These vibrations are picked up by the ear
1) An object makes a sound by vibrating

2. 23/11/2018

3. What is sound?
Sound is a compressional wave which travels through the air through a series of compressions and rarefactions.

4. Compare a longitudinal wave in a slinky to a sound wave in a tube:

9. A = pressure amplitude = max. change in pressure
very small for common sounds ( 3x10-2 Pa)
Loudness is related to pressure amplitude

10. Characteristics of Sound
Sound can travel through any kind of matter, but not through a vacuum.
Sound can travel through any kind of matter, but not through a vacuum.
The speed of sound is different in different materials; in general, it is slowest in gases, faster in liquids, and fastest in solids.
The speed of sound is different in different materials; in general, it is slowest in gases, faster in liquids, and fastest in solids.
The speed depends somewhat on temperature, especially for gases.
The speed depends somewhat on temperature, especially for gases.

11. Measure V sound with Vernier – wooden block clap
Ti= s
Tf= s
Tf-Ti= s
Tube length L = 1.7m (?)
V sound =318 m/s
Main error in L value

12. Frequency (Pitch) of Sound Waves: number of cycles per second
Healthy young ears can hear frequencies between:
20 Hz
20,000 Hz
Infrasonic
Which end do we lose with age?
Ultrasonic
Pure tone – a single frequency sound
(most sounds are composed of many frequencies)

13. See Audio Sweep Generator software

14. Speed of Sound depends on the medium (gas, liquid or solid)
vsound in air = 343 m/s
Ex: Lightning & Thunder
How can you tell how far away the storm is ??

15. Echo calculations…

18. Ultrasound
Ultrasound is the region of sound above 20,000Hz – it can’t be heard by humans. There are a number of uses for ultrasound:
Pre-natal scanning
2) Echo sounding

19. How does ultrasound work?
Ultrasonic waves are partly _________ at the boundary as they pass from one _______ to another. The time taken for these reflections can be used to measure the _______ of the reflecting surface and this information is used to build up a __________ of the object.
Words – depth, reflected, picture, medium

22. What is sonar?
Sonar is a system that uses the reflection of underwater sound waves to detect objects. This has been used to find sunken ships and schools of fish.

23. Some interesting applications of Sound Waves
Sonar:
Ex: Dolphins
Ex: Web Link: Ocean floor mapping
Ultrasound:
Web Link: How does Ultrasound work?
Cancer treatment:
Web Link: Local Hyperthermia