Come on. The speed of sound is not a physical constant as it depends on the temperature and the humidity. So it is safe to make an approximation of 333 m/s to estimate the distance of a lightning, especially practical for computing mentally. Moreover, the space between the lightning and our ear goes into many regions of different air density.
John Altounji One size does not fit all. Social promotion ruined Education. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Saturday, June 29, 2013 2:48 PM To: U.S. Metric Association Cc: U.S. Metric Association Subject: [USMA:53007] RE: Flash To Bang (Lightning Distance) Assume? I rarely assume, but I did look it up. According to https://en.wikipedia.org/wiki/Speed_of_sound The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at 20 °C the speed of sound is 343.2 metres per second. Where do you get 333 m/s? David Pearl MetricPioneer.com 503-428-4917 ----- Message from [email protected] --------- Date: Wed, 26 Jun 2013 20:17:21 +0100 From: Martin Vlietstra <[email protected]> Reply-To: [email protected] Subject: [USMA:52992] RE: Flash To Bang (Lightning Distance) To: "U.S. Metric Association" <[email protected]> > Assume that sound travels at 333 m/s. The sound will travel one > kilometre in three seconds. > > > From: [email protected] [mailto:[email protected]] On > Behalf Of John M. Steele > Sent: 26 June 2013 12:45 > To: U.S. Metric Association > Subject: [USMA:52990] Flash To Bang (Lightning Distance) > > > Interesting article on estimating the distance to a thunderstorm: > > http://www.livescience.com/37734-how-far-away-is-lightning-distance.ht > ml > > > She starts with the usual 5 seconds per mile, but she does include a > metric version. I'm not sure I want to multiply by 340 m/s in my head, however. > It might be easier to just divide by 3 for an approximate (and > slightly > conservative) distance in kilometers. > > > She mentions, but perhaps doesn't adequately explain, the variation of > the speed of sound with temperature. That may be why she gives two > values, only one sentence apart. The lower figure is correct at 0 °C, > the higher figure near 20 °C (remember it is cooler aloft, so the > sound is arriving via multiple paths with differing, generally unknown, temperature profiles). > ----- End message from [email protected] -----
