(Lansing State Journal, July 28, 1993)
Question submitted by Aaron Maike.
While both light and sound travel as waves, the speed of light is much, much faster.
Light is composed of electromagnetic waves which travel independent of a medium. That is to say, light can travel in a vacuum, such as outer space. Electromagnetic waves travel very fast. In a vacuum, the speed is 300,000,000 meters per second; the maximum speed which energy may obtain. This value is abbreviated as "c" , and you may have seen it before as part of Einstein's equation E=mc2. However, when light passes through transparent materials, it slows down a bit. This is because electromagnetic waves interact with the subatomic components of matter. In water, for example, light slows down to around 0.75c, or 225,000,000 meters per second. Even in a material as dense as diamond light travels well over 100 million meters per second!
Sound is created by small changes in pressure near the surface of a vibrating object. These changes are propagated through a material medium, such as air, like the ripples formed when one tosses a stone into a pool of water. Sound travels through air at about 340 meters per second. In contrast to light, sound often travels faster in dense materials. In liquid water, sound travels 1450 meters per second. And, in metals such as iron, sounds can travel well over 5000 meters per second. While this is about ten times the speed of a supersonic jet airplane, it is only a tiny fraction of the speed of light.