Sound

Sound is a form of energy produced when an object vibrates. These vibrations create pressure waves that travel through a material such as air, water or a solid. Unlike light, sound cannot travel through a vacuum because it needs particles to carry the vibrations from one place to another. The speed of sound depends on the medium.

In dry air at 20 °C, it travels at about 343 metres per second, while it moves much faster through liquids and solids because their particles are packed more closely together. The frequency of a sound determines its pitch, while its amplitude is related to how loud it is. Humans can usually hear frequencies between about 20 hertz and 20,000 hertz.

Sound plays an essential role in everyday life, communication and technology. The human ear collects sound waves and converts them into electrical signals that the brain interprets as voices, music or other sounds. Echoes occur when sound waves reflect from a surface, while ultrasound uses frequencies above the range of human hearing.

Ultrasound is widely used in medicine to produce images of organs and developing babies, and it also helps measure distances or detect objects underwater using sonar. Engineers study sound to improve concert halls, reduce unwanted noise and design better speakers, microphones and musical instruments. Understanding how sound behaves has led to advances in science, medicine, communication and many modern technologies.