By Smithsonian's National Air and Space Museum
Sound is created when something moves and disturbs the air around it, like a drum being hit or a person’s vocal cords vibrating.
This disturbance travels through the air in waves as neighboring particles bump into each other until it reaches your ear and your brain translates it into sound. This pattern of disturbance is called a sound (or pressure) wave.
Sound also travels through liquids and solids. It travels most slowly through a gas like the air around us, but more quickly through liquids and fastest of all through solids.
When we talk about the speed of sound, we’re normally talking about the speed of sound through the air. The speed of sound in air is about 767 mph (1,235 km/h) at sea level.
The speed that sound waves travel depends on the air particles so conditions that change how the particles are behaving will affect the speed of sound, like temperature.
As air particles move more slowly at low temperatures and faster at high temperatures, a sound wave will travel faster when it’s warm and slower when it’s cold.
If something moves faster than the speed of sound, it is said to break the sound barrier. As it gets colder the higher up in the atmosphere you go, it becomes easier for an aircraft to move faster than sound.
artsandculture.google.com