SPEED OF SOUND
The frequency of a sound wave is a measure of the number of waves passing a given point in one second. The distance between two successive crests of the wave is called the wavelength. The product of the wavelength and the frequency equals the speed of the wave. The speed is the same for sounds of all frequencies and wavelengths (assuming the sound is propagated through the same medium at the same temperature). The speed of sound in dry, sea level air at a temperature of 0°C (32°F) is 332 m/sec (1,088 ft/sec). The speed of sound in air varies under different conditions. If the temperature is increased, for example, the speed of sound increases; thus, at 20°C (68°F), the speed of sound is 344 m/sec (1,129 ft/sec). The speed of sound is different in other gases of greater or lesser density than air. The molecules of some gases, such as carbon dioxide, are heavier and move less readily than molecules of air. Sound progresses through such gases more slowly. Conversely, sound travels through helium and hydrogen faster than through air because atoms of helium and hydrogen are lighter than molecules of air.
Sound generally moves much faster in liquids and solids than in gases. In both liquids and solids, density has the same effect as in gases. The speed of sound also varies directly as the square root of the elasticity of the medium. Elasticity is the ability of a substance to regain its original shape and size after being deformed. The speed of sound in water, for example, is slightly less than 1,525 m/sec (5,000 ft/sec) at ordinary temperatures—almost five times as fast as in air. The speed of sound in copper, which is more elastic than water, is about 3,350 m/sec (about 11,000 ft/sec) at ordinary temperatures. In steel which is even more elastic sound moves at a speed of about 4,880 m/sec (about 16,000 ft/sec). Sound is propagated very efficiently in steel.
