Flash to Bang Distance Formula

[SWEATYSOCK]

Was watching a firework display the other night and was explaining to my son that you can calculate the distance you are from the display by timing the difference between seeing the flash then hearing the bang. Unfortunately I couldnt remember the equation !
Believe it works for thunderstorms and Naval gunfire too.
I'm sure one of you old seadogs will know it well enough.
Thanks,SS.

 

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[Real de Tayopa Tropical Tramp]

HI 1100 ft per sec at sealevel, normal temp.

Don Jose de La Mancha

 

[deepskyal]

One Mississippi, two mississippi.......

Al

 

[Hemisteve]

One Missis.......Dang, that was close!!!

 

[SomeGuy]

From Army Field Manual FM 21-75:

FLASH-AND-SOUND METHOD (BEST AT NIGHT)

Sound travels through air at 300 meters (1,100 feet) per second. That makes it possible to estimate distance if you can both see and hear a sound-producing action.

When you see the flash or smoke of a weapon, or the dust it raises, immediately start counting. Stop counting when you hear the sound associated with the action seen. The number at which you stop should be multiplied by three. This gives you the approximate distance to the weapon in hundreds of meters. If you stop at one, the distance is about 300 meters. If you stop at three, the distance is about 900 meters. When you must count higher than nine, start over again after counting nine (counting higher numbers throws the timing off).

 

[dcinffxva]

Roughly 1/5 of a mile for every second, so 5 seconds = 1 mile. Same as the post above says, but without trying to figure out meters. Sound actually travels 5,500 feet in 5 seconds, and a mile is only 5,280 feet, but still a pretty close guesstimate.

 

[greydigger]

isn't the spped of sound also called mach 1 ?

 

[boogeyman]

Unless you're at a fireworks show. The rule is observe the flash, then grab some cover!