speed of light v. speed of sound

Speed of Light

The speed of light is 299,792,458 meters per second, or approximately 1 billion kilometers per hour (670 million miles per hour). Represented by the letter c, it is the speed at which electromagnetic radiation propagates in a vacuum. It is also the maximum speed at which matter, energy, or information can travel.

The speed of light is a fundamental physical constant, and remains the same for observers in all inertial reference frames. When light moves through transparent materials, it is constantly absorbed and re-radiated, making its average speed in a medium less than c.

Speed of Sound

The speed of sound in air at 20° C, also called Mach 1, is 343 meters per second (1,236 kilometers per hour, or 768 miles per hour). This makes light about 900,000 times faster than sound. For phenomena occurring within several kilometers of an observer, light’s travel time will be perceived as functionally instantaneous, but sound from the same source will arrive about 3 seconds later for every kilometer separating the observer from the event.

Unlike electromagnetic radiation, sound requires a medium through which to travel, and its speed varies depending on the composition and temperature of that medium. The speed of sound increases with increasing stiffness, decreasing density, and increasing temperature. Sound travels faster in liquids than gases, and faster still in solids.