# Fascinating Facts About The Speed Of Sound

• It was British scientist Sir Isaac Newton who gave the first analytical determination of the speed of sound in his scientific treatise, “Principia,” in 1687.
• But it was Italian physicists Giovani Alfonso Borelli and Vincenzo Viviani who, in the 1660s, first calculated the speed of sound. They measured the time between seeing the flash of a gun and hearing its report over a long distance on a still day. Their calculation: 350 meters per second.
• Although the equation for the speed of sound (speed = frequency x wavelength) is constant, the speed is affected by the medium through which the sound waves are propagated, as well as other conditions such as temperature and humidity.
• Today's accepted value for speed of sound through air: 344 m/s (1,130 feet per second).
• The first measurement of the speed of sound through solids didn't come until the early 1800s, through the experiments in sound frequency of German physicist and musician Ernst Florens Friedrich Chladni, often called the father of acoustics.
• Speed of sound through most solids: 5,960 m/s (13,332 mph).
• Soon after, in 1826, Swiss physicist Daniel Colladon calculated the speed of sound in 8 degree Centigrade water as 1,435 m/s.
• Today's calculation of speed of sound through water at that temperature: 1,482 m/s (3,315 mph).
• Why is light so much faster than sound? Light is an electromagnetic wave, and its photons can move as a wave through air or as particles through a vacuum. Sound, however, is a pressure wave, which must produce a vibration to be heard. That can only occur when the wave encounters a particle of some kind, such as an air molecule.
• The Doppler Effect is the change in the perceived frequency of sound waves. If the source of a sound and the listener are standing still, the sound waves are emitted in uniform concentric circles. But if the source moves toward the listener, the waves reaching the listener are closer together, and the listener hears a higher frequency.
• When an aircraft travels through air at less than the speed of sound, about 770 mph, the sound waves it produces propagate ahead of it. But when it travels at supersonic speed, the distance between sound waves decreases to nothing, and they combine to create a sonic boom.
• Flicking the tip of a bullwhip also creates a sonic boom, as does thunder.
• An echo, or reflection, occurs when sound waves bounce off a surface. A ship in a fog can avoid running into cliffs by sounding a foghorn and waiting for the echo. If the time delay is, say, 1.5 seconds, and using 330 m/s as the speed of sound, the ship would be about 250 meters from the cliffs.
• You can't see around a corner because light waves don't bend. But you can hear around a corner because of wave diffraction: If the wavelength of a wave is similar to the size of an object, it bends around it and spreads out as it passes.

Sources: www.britannica.com,www.americanscientist.org, how stuffworks.com, “Audio Engineering for Sound Reinforcement” by John Eargle and Chris Forman, ©2002.

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