# Is the speed of sound constant?

I was looking at lightning, and started to wonder if the speed of the thunder slowed down as it lost energy traveling far distances. I know the amplitude of sound decreases, perceived as volume. Im not certain, however, how to actually calculate the distance of a lightning strike based off of of the interval of time between observing the flash and hearing the thunder. Would this time be linear ( is the speed of sound constant?), or is it non-linear (Speed of sound loses velocity over time?)

If I were to determine this by comparing two audio recordings of the same lightning strikes' thunder, and seeing if the further one was lower in frequency, would that accurately indicate a deceleration of the sound?

• Regarding the 2nd paragraph: if the speed of sound slows down, does the frequency get lower or does the wavelength get shorter (or both or neither)? Hint: Snell's Law and wavefronts.
– JEB
Feb 19, 2018 at 0:56
• The speed of sound should not vary with the "energy" left in the travelling wave. The energy only changes the frequency and wavelength. The speed completely depends on the medium in which the wave is travelling. Feb 19, 2018 at 1:17
• The speed of sound in air is dependent on the temperature, pressure, and moisture content of the air. (And likely on the CO2 concentration as well.) Feb 19, 2018 at 2:16
• @probably_someone - I wonder where you found a dispersion relation of sound in air that gives you a speed of sound that depends on frequency. Feb 19, 2018 at 2:34
• @freecharly My mistake, comment is now rightfully deleted. Feb 19, 2018 at 2:45