Sound can be described as a pressure disturbance that travels through the constituent particles of a medium: as one particle of the medium is perturbed by the pressure, it exerts a force on an adjacent particle, thus perturbing that particle in turn....

The distance through a defined medium covered by a sound wave per unit time. The speed varies with the medium through which the energy is transmitted and its density. In air at standard temperature and pressure the speed of sound is 344 m/sec....

The speed of sound is variable and depends mainly on the temperature and the properties of the substance through which the wave is traveling. For example, in low molecular weight gases, such as helium, sound propagates faster compared to heavier gases,...

Today is Friday, April 20, the 110th day of 2007. There are 255 days left in the year.Today's Highlight in History:On April 20, 1999, the Columbine High School massacre took place in Littleton, Colo., as two students shot and killed 12 classmates and one teacher...

Today is Monday, Oct. 15, the 288th day of 2007. There are 77 days left in the year.Today's Highlight in History:On Oct. 15, 1917, Dutch dancer Mata Hari, convicted of spying for the Germans, was executed by a French firing squad outside Paris.On this date:In...

Pilot Scott Crossfield, the first man to fly at twice the speed of sound, and an air traffic controller were blamed Thursday for the crash of a single-engine plane during a thunderstorm last year that killed Crossfield.A test pilot who personified "the right stuff" during...

Today is Saturday, Oct. 13, the 286th day of 2007. There are 79 days left in the year.Today's Highlight in History:On Oct. 13, 1792, the cornerstone of the executive mansion, later known as the White House, was laid during a ceremony in the District of...