Editing Speed of sound (section)

===Practical application to air===
By far, the most important factor influencing the speed of sound in air is temperature. The speed is proportional to the square root of the absolute temperature, giving an increase of about {{val|0.6|u=m/s}} per degree Celsius. For this reason, the pitch of a musical wind instrument increases as its temperature increases.

The speed of sound is raised by humidity. The difference between 0% and 100% humidity is about {{val|1.5|u=m/s}} at standard pressure and temperature, but the size of the humidity effect increases dramatically with temperature.

The dependence on frequency and pressure are normally insignificant in practical applications. In dry air, the speed of sound increases by about {{val|0.1|u=m/s}} as the frequency rises from {{val|10|u=Hz}} to {{val|100|u=Hz}}. For audible frequencies above {{val|100|u=Hz}} it is relatively constant. Standard values of the speed of sound are quoted in the limit of low frequencies, where the wavelength is large compared to the mean free path.<ref>{{cite web
| url = http://www.phy.mtu.edu/~suits/SpeedofSound.html
| title = Speed of Sound in Air
| publisher = Phy.mtu.edu
| access-date = 13 June 2014
| archive-date = 23 June 2017
| archive-url = https://web.archive.org/web/20170623092133/http://www.phy.mtu.edu/~suits/SpeedofSound.html
| url-status = dead
}}</ref>

As shown above, the approximate value 1000/3 = 333.33... m/s is exact a little below {{val|5|u=degC}} and is a good approximation for all "usual" outside temperatures (in temperate climates, at least), hence the usual rule of thumb to determine how far lightning has struck: count the seconds from the start of the lightning flash to the start of the corresponding roll of thunder and divide by 3: the result is the distance in kilometers to the nearest point of the lightning bolt.  Or divide the number of seconds by 5 for an approximate distance in miles.