Vibrations that travel through the air or another medium and can be heard when they reach a person's or animal's ear. Sound is a form of energy.
How Sound Travells
When an object vibrates, then the air layers around it also starts vibrating in exactly same way and carry sound waves from producing object to our ears. Sound waves needs a materal medium like solid liquid or gas to travel and to be heared. Sound cannot travel through vacuum. Sound cannot be heard on the surface of moon because there is no air on the moon to carry sound waves.
The Speed of Sound
The speed of sound depends on:
- The nature of material through which it travels.
- The temprature: The speed of sound in air is more on a hot day then on a cool day.
- The humidity of air: The speed of sound is less in dry air but more in humid air.
On a rainy day the flash of lightning is seen first and the sound thunder is heard a little because the speed of light is very high, thats why we see the flash of lightning first.
The repetition of sound caused by the reflection of sound waves is called and echo. An echo is simply a reflected sound. The bouncing back of sound when it strikes a hard surface is called as reflection of sound.
Hearing Range of Human Ears
Our ears can hear a sound of frequency 20 Hz to 20000 Hz. It is the audible range of frequencies for human ears.
The sound having too high frequency which cannot be heard by human beings are called ultrasonic sound or ultrasound.
Thw word 'SONAR' stands for 'Sound Navigation and Ranging'. Sonar is an apparatus which is used to find the depth of a sea or to locate the underwater things like shoals of fish, shipwrecks and enemy submarines.