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Although it may look like this F-14A Tomcat is burning enough oil to fuel America's automotive enthusiasts for a decade, there's no need to call OPEC yet. In fact, this plane has just broken through the sound barrier and the "smoke" is actually water vapor created by shock waves.

The speed of sound is 758 miles per hour in air that is 68 degrees Fahrenheit. This speed varies according to atmospheric conditions because sound moves faster through liquids than it does through gases.

As an airplane approaches the speed of sound, it "pushes" the sound waves that are in front of it. Because sound cannot travel faster than itself, sound waves "pile up." These compressed waves of sound are called "shock waves." As shock waves move away from the airplane, they cause pressure to drop. This pressure drop causes water to vaporize and the human ear to perceive a loud "sonic boom."

Air Force Captain Chuck Yeager first broke the sound barrier on Oct. 14, 1947. After this initial break-through (please excuse our pun), aircraft traveled faster and faster until, on Oct. 3, 1967, Air Force Captain Peter Knight piloted his X-15 to a new record: 4,690 miles per hour--nearly 7 times the speed of sound.

Photograph by PH2 Hensley. Courtesy Defense Visual Information Center.


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			In Need of a Tune-up? Although it may look like this F-14A Tomcat is burning enough oil to fuel America's automotive enthusiasts for a decade, there's no need to call OPEC yet. In fact, this plane has just broken through the sound barrier and the "smoke" is actually water vapor created by shock waves. The speed of sound is 758 miles per hour in air that is 68 degrees Fahrenheit. This speed varies according to atmospheric conditions because sound moves faster through liquids than it does through gases. As an airplane approaches the speed of sound, it "pushes" the sound waves that are in front of it. Because sound cannot travel faster than itself, sound waves "pile up." These compressed waves of sound are called "shock waves." As shock waves move away from the airplane, they cause pressure to drop. This pressure drop causes water to vaporize and the human ear to perceive a loud "sonic boom." Air Force Captain Chuck Yeager first broke the sound barrier on Oct. 14, 1947. After this initial break-through (please excuse our pun), aircraft traveled faster and faster until, on Oct. 3, 1967, Air Force Captain Peter Knight piloted his X-15 to a new record: 4,690 miles per hour--nearly 7 times the speed of sound. Photograph by PH2 Hensley. Courtesy Defense Visual Information Center.