1. Sound is a form of energy.

2. Requirements to produce sound :

3. The medium provides "particles" to transmit the sound energy. Therefore sound cannot travel through a vacuum since a vacuum does not have any "particles".

4. Sound is not transmitted by "particle" means but rather as a longitudinal wave. The particles allow for the creation of these longitudinal waves by vibrating. Sound is able to display interference, both constructive and destructive.

5. Sound travels fastest through solids, slower through liquids and the slowest through gases. Gases with higher densities transmit sound better.

6. Sound is a transmitter of energy.

7. The speed of sound through air is approximately 330ms-1.
This speed is called Mach 1.
When an object travels faster than Mach 1 it is said to have broken the sound barrier.

8. Two factors affect the speed of sound in a medium :

Both factors operate simultaneously. Although metals have very high densities compared to gases, the "slowness of the sound" as a result of the densities is overpowered by the metal's very high elasticity. Hence sound is faster in metals than in liquids or gases.

9. The higher the temperature of a gas, the faster will be the speed of sound in that gas.

10. Sound can reflect off substances. When a sound wave strikes a surface, it is divided into three parts :

11. Echo: If a person stands far from a surface that reflects sound easily, the original sound and the reflected sound can be heard separately. This effect is called an echo.

12. Reverberations occur when the original sound and the reflected sound almost coincide, creating a prolonged sound. Acoustics is the science involved in the design of halls for performances, recording studios etc. to prevent too much or too little reverberation.

13. Sonar is an underwater detection device that uses reflection of sound waves to detect objects.
It stands for Sound Navigation and Ranging.
A bat navigates by a built-in sonar device.

14. A seismograph is an instrument used by geologists to detect echo patterns produced when waves from an explosion on the surface of the Earth is reflected by various underground objects.

15. Parabolic reflectors are used to focus sound to a specific point.

16. Since sound is a wave, it can refract.
Changes in air temperature or density causes sound waves to refract.

17. Resonance: All objects have a natural frequency of vibration. When an object vibrates at this natural frequency as a result of another object already vibrating at this same frequency, the phenomenon is called resonance.

18. As the frequency of a sound increases, the pitch increases.

19. The normal human hearing range is from 15Hz to 20kHz (20 000 Hz).
Sounds of frequency higher than 20 000Hz are termed ultrasonic and cannot be heard by the human ear.
An ultrasonic pulse is emitted by a sonar device, and ultrasonic sound waves are used in the field of medicine.

20. As the amplitude increases, the loudness increases.

20. The loudness of sound is measured in the units dB (decibels).

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