Sound travels in waves from a transmitter to a receiver through a medium. The wave is produced by the vibration of particles in mediums such as gases, liquids and solids. Because sound requires a medium of interconnected and interactive particles, it cannot travel in a vacuum such as space.
The source of the sound sets off a chain of events by vibrating the particle of the medium that is closest to it. This first particle that starts vibrating because of the energy it received from the source transfers its energy to the next closest particle, thus causing a second particle to vibrate. The second particle then transfers its energy to its closest neighbor. This process of energy transfer allows sound to travel from its source to the observer.
The medium through which sound travels determines its speed. It travels faster in solid mediums than in liquid and faster in liquid mediums than in gases. However, when sound travels through gas, its speed is also temperature-dependent. Because the air at sea level is denser than at a high altitude, sound travels faster at sea level.
Sound waves move in patterns known as compressions. Normally sound travels in a straight line, but it also bounces off objects it encounters, and this reflection is called an echo. As sound waves travel, they lose energy. For this reason, sounds generated at a distance are difficult to hear. In measuring sound waves, amplitude has to do with the height of the waves, and frequency measures the number of sound waves produced in a second. The amplitude and frequency of sound give it diversity. High amplitude sounds are louder than low amplitude. Soprano singers and violins are high frequency, while bass sounds are low frequency.