VELOCITY AND WAVELENGTH

Two other characteristics of waves are important: the velocity and wavelength.The velocity of a wave is simply how fast the wave moves,and is commonly measured in meters per second (m/s).Sound waves propagate through the air at approximately 343 m/s,or about 767 miles per hour.At this peed, the sound waves travel one mile in about five seconds.While the speed of sound is generally considered constant,it is not a truly constant value.The actual velocity varies slightly depending on the temperature and the density of the air.Sound will therefore travel at different speeds at different altitudes and in different atmosphericconditions. For practical purposes,however,343 m/s is an accurate value for the speed of sound waves that we hear in everyday life,and we can consider this value to be constant.The letter 'v' is commonly used to denote velocity.Waves are often modelled mathematically by the sine function. It may be easy to see why.Many waves that we see in real life take on the shape of a sine curve.Waves on the surface of water,for instance,or waves travelling down a rope generally have a shape that is very similar to the sine function.Sound waves,because of their nature, do not have this specific shape,but they can still be modelled by a sine curve.Picture a sound wave, as in the diagram,with a sine curve drawn next to it.The regions of compression could correspond to the peaks of the sine wave and the rarefactions could correspond to the troughs. Mathematically,this comparison is perfectly valid,and allows sound waves to be dealt with mathematically using the sine function.The wavelength is the distance between two individual wave fronts.For waves on the surface of a pond, the wavelength is easy to see.It is simply the distance between two peaks,or the distance between two troughs.For a sound wave,the wavelength is the distance between two compressions, which is the same as the distance between two rarefactions.Wavelength is commonly measured in meters.Wavelength is directly related to frequency.If sound waves are being produced at a very high frequency, each wave will not have time to travel very far before the next one is emitted right behind it.The wavelength will consequently be relatively short.In general,the higher the frequency,the shorter the wavelength.The reverse is also true:lower frequency waves have larger wavelengths.The Greek letter "lambda",is commonly used to denote wavelength.Mathematically,the relationship between velocity,frequency, and wavelength is given by the equation velocity = frequency x wavelength Higher frequency sounds, therefore, have a shorter wavelength.If the wavelength is short, then the individual wave fronts must be close together.Since they are close together,many of them strike your ear in a given second, and you hear a high frequency.