Sound · ध्वनि
A free Physics lesson for Class 9 children.
Sound is produced by vibrating objects and needs a medium to travel.
Sound cannot travel through a vacuum.
In air, sound travels as a longitudinal wave of compressions and rarefactions.
Wavelength is the distance between two neighbouring crests.
Frequency is the number of vibrations in one second. Its unit is hertz.
The speed of a wave equals its frequency multiplied by its wavelength.
Loudness depends on amplitude, and pitch depends on frequency.
An echo is sound reflected back from a surface such as a wall or a cliff.