1. 16.2 Properties of sound waves How sound travels Can sound travel through solids or liquids? Yes.

2. 16.2 Properties of sound waves In a tin can phone, sound can be transmitted via a string, which is a solid. Dolphins communicate by sending sound underwater.

3. 16.2 Properties of sound waves to power supply bell jar electric bell to vacuum pump Sound waves cannot travel through a vacuum.  The sound of the electric bell becomes quieter when the amount of air in the jar decreases.  No sound can be heard when it is a vacuum inside the jar. ∵ Sound waves require a medium for transmission. Video: Can sound waves travel through a vacuum?

4. 16.2 Properties of sound waves  Astronauts cannot communicate directly by sound waves.  Radio systems – the sound signals are carried by radio waves which can travel through a vacuum.

5. 16.2 Properties of sound waves Speed of sound The first car in the world that can travel faster than the speed of sound in air. Do you know how fast the sound travels in the air?

6. 16.2 Properties of sound waves  speed of sound in air microphones timer  The timer measures the time taken for the sound wave to travel between the microphones.

7. 16.2 Properties of sound waves In an orchestra performance, the sounds from different instruments which have different frequencies and loudness reach our ears at the same time.

8. 16.2 Properties of sound waves  The speed of a sound does not depend on its frequency or loudness.  Temperature can affect the speed of sound. e.g. At 0 ºC, the speed of sound in dry air = 331 m s –1. As temperature increases, the speed of sound also increases.

9. 16.2 Properties of sound waves  The speed of sound also depends on the medium in which it travels. In general, speed of sound follows this order: solids > liquids > gases MediumSpeed (m s –1 ) Gases– Carbon dioxide (0 ºC)258 Air (0 ºC)331 Air (20 ºC)344  Speeds of sound in different materials:

10. 16.2 Properties of sound waves MediumSpeed (m s –1 ) Liquids– Mercury (20 ºC)1451 Water (0 ºC)1402 Water (20 ºC)1482 Water (100 ºC)1543

11. 16.2 Properties of sound waves MediumSpeed (m s –1 ) Solids– Lead1960 Copper3100 Gold3240 Brick3650 Wood4000 Glass4540 Iron5000 Steel5941 Aluminium6420

12. 16.2 Properties of sound waves Frequency of sound waves  Frequency of sound waves produced = Frequency at which the source vibrates  Tuning forks can produce sound waves of particular frequencies.

13. 16.2 Properties of sound waves the frequency of sound produced the note produced

14. 16.2 Properties of sound waves  The human ear can detect sound waves of frequencies within the human audible frequency range –  age approximately 20 Hz to 20 000 Hz. Simulation: Testing your audible frequency range ability to hear high frequency sound

15. 16.2 Properties of sound waves  The audible frequency ranges for some animals: AnimalAudible frequency range (Hz) bats1000 – 150 000 cats100 – 32 000 dogs40 – 46 000 dolphins70 – 150 000 elephants16 – 12 000 horses31 – 40 000

16. 16.2 Properties of sound waves That’s the end of Section 16.2 Check Point Key Ideas Previous Page Section 16.3 Exit