Sound is a type of energy that travels through the air, or any other medium, as a vibration of pressure waves. Sound is the sensation produced when these waves strike the ear. The study of sound, known as acoustics, is important in many fields including engineering, architecture, and medicine.
Sound is produced when an object vibrates. The vibrations cause molecules in the surrounding medium to collide with each other and produce wave-like disturbances. For example, when a tuning fork is struck, it vibrates and sets the air molecules around it into oscillation. These oscillating molecules then bump into other air molecules, causing them to vibrate too. This process continues until the sound waves eventually reach our ears.
The human ear can detect a very wide range of frequencies of sound vibrations – from about 20 Hz up to 20 kHz. However, we are most sensitive to frequencies between 2 kHz and 5 kHz (kilohertz), which are within the range of human speech. The loudness or intensity of a sound wave is measured in decibels (dB). A whisper has an intensity level of about 30 dB while a jet engine has an intensity level around 140 dB.
The pitch of a sound depends on its frequency – how often per second the particles vibrate back and forth past a given point. A low-pitched sound has fewer vibrations per second than a high-pitched one; for example, bass notes on a piano have lower frequencies than treble notes. The pitch also varies depending on how loudly the note is played; for instance, playing middle C (C4) softly produces a different pitch than playing it loudly (forte). In general terms, however, we perceive higher pitched sounds as being louder than lower pitched ones because our ears are more sensitive to higher frequencies