Sound · ध्वनि
A free Physics lesson for Class 8 children.
Sound is produced by vibrating bodies. A plucked string, a drum skin and our vocal cords all vibrate.
Sound needs a medium to travel: a solid, a liquid or a gas. It cannot travel through a vacuum.
The number of vibrations per second is the frequency, measured in hertz. The maximum displacement is the amplitude.
Loudness depends on the amplitude: a bigger amplitude means a louder sound. Pitch depends on frequency: higher frequency, higher pitch.
We hear sounds between about 20 Hz and 20 000 Hz. Unwanted, unpleasant sound is noise, and too much of it is noise pollution.