1. Sound Speed and Frequency: Learning Goal
The student will be able to explain the nature between the speed of sound in various media and the particle nature of the media and explain selected natural phenomena (echolocation, infrasound/ultrasound) with reference to the characteristics and properties of waves (E3.5, E3.6).

2. Sound Speed and Frequency
3U Physics

3. The Speed of a Wave
As demonstrated by the slinky waves, the speed at which a wave propagates is dependent on the properties of the medium.

4. Sound Waves
Remember that sound is a pressure wave. A vibration (e.g. of a tuning fork) bumps air particles, which bump the air particles next to them, etc.

5. Sound in Air
Sound travels faster in warmer air (in which the particles are faster-moving):

6. Sound in Air: Example
Example: You see a flash of lightning from a storm 1.4 km away and hear the crack of lightning 4.0 s later. What is the temperature of the air?

7. Sound in Air: Example
Example: You see a flash of lightning from a storm 1.4 km away and hear the crack of lightning 4.0 s later. What is the temperature of the air?

8. Sound in Air: Example
Example: You see a flash of lightning from a storm 1.4 km away and hear the crack of lightning 4.0 s later. What is the temperature of the air?

9. Sound in Air: Example
Example: You see a flash of lightning from a storm 1.4 km away and hear the crack of lightning 4.0 s later. What is the temperature of the air?

10. Sound in Air: Example
Example: You see a flash of lightning from a storm 1.4 km away and hear the crack of lightning 4.0 s later. What is the temperature of the air?

11. Sound in Air: Example
Example: You see a flash of lightning from a storm 1.4 km away and hear the crack of lightning 4.0 s later. What is the temperature of the air?

12. Sound in Air: Example
Example: You see a flash of lightning from a storm 1.4 km away and hear the crack of lightning 4.0 s later. What is the temperature of the air?

13. Sound in Liquids and Solids
And sound will also travel faster in denser materials (liquids and solids).
E.g. the speed of sound in water is typically m/s.

14. Sound in Liquids and Solids
And sound will also travel faster in denser materials (liquids and solids).
E.g. the speed of sound in water is typically m/s.
A swimmer 1500 m away from a loud sound would hear it the sound 1 s later through the water or more than 4 s later through the air.

15. Echolocation: Example
Example: A dolphin sends out a pulse at a frequency of Hz and hears an echo back from an object 2.4 s later. How far away is the object?

16. Echolocation: Example
Example: A dolphin sends out a pulse at a frequency of Hz and hears an echo back from an object 2.4 s later. How far away is the object?

17. Echolocation: Example
Example: A dolphin sends out a pulse at a frequency of Hz and hears an echo back from an object 2.4 s later. How far away is the object?

18. Echolocation: Example
Example: A dolphin sends out a pulse at a frequency of Hz and hears an echo back from an object 2.4 s later. How far away is the object?

19. Frequency
The frequency of any sound wave is always the frequency of the source and does not change or affect the speed of the wave as it propagates.

20. Frequency
The frequency of any sound wave is always the frequency of the source and does not change or affect the speed of the wave as it propagates.
(Changing the speed will change the wavelength, not the frequency.)

21. Frequency
Humans can hear sounds between about 20 and Hz (though most humans lose the ability to hear very high frequencies by the time they are teenagers).
Most human speech is between 200 and Hz, and the ear is most sensitive to frequencies between 1000 and 3500 Hz.

22. Ultrasound Sound above 20 000 Hz is called ultrasound.
A common use of ultrasound is range finding under water: i.e. echolocation or sonar.

23. Ultrasound
Diagnostic medical ultrasonograms work on the same principle.

24. Infrasound
Sound below 20 Hz is called infrasound, which may be produced by events such as earthquakes.
Some animals such as elephants use infrasound for communication, even over long distance.

25. Infrasound
While humans cannot consciously detect infrasound, they may still be sensitive to the vibrations:
In particular, infrasound is known evoke feelings of awe and fear, and frequencies close of 18 Hz, the resonant frequency of the eye, may cause optical illusions of “ghosts.” Infrasound may be responsible for many alleged “hauntings.”

26. Frequency and Pitch
Within the audible range, frequency of a sound wave is commonly referred to as the pitch of the sound.
A high-frequency sound wave has a high pitch.
A low-frequency sound wave has a low pitch.

27. Frequency and Noise
A sound wave of a single frequency will be heard as a distinct tone or note.
Irregular sound waves will be heard as noise.