Explain sound and loudness.

A sound is a form of energy produced by vibrating bodies. Sound is produced when something vibrates. The vibrating body causes the medium (water, air, etc.) around it to vibrate. Vibrations in the air are called travelling longitudinal waves, which we can hear.

At 20 °C, the speed of sound in air is about 343 meters per second.

Loudness is the attribute of sound that determines the intensity of auditory sensation produced. When the intensity is very small, the sound is not audible; when it is too great, it becomes painful and dangerous to the ear.