Thunder, lightning and distance.

Factual Questions
1

Well I’m just witnessing one hell of a thunderstorm right now.

It got me thinking, I was always told once you saw the sky “light-up” with lightning, you could count the seconds until the thunder sounded and you could tell how far away the lightning was. 1 second = 1 mile.

Is there any truth to this?

MtM

2

Actually, the rule-of-thumb is 5 seconds=1 mile. Which isn’t far off. Sound travels in air at STP at 1087 feet per second. There are 5280 feet in a mile, which works out to 4.86 seconds per mile.

3

Not one second per mile but five seconds per mile.

Sound travels at 331.29 meters per second (at a set temperature at a set air pressure at sea level yadda yadda), which is about 1,087 feet per second which is just over 1/5 of a mile.

4

No, the speed of sound is about 776 mph (1,240 kph for non-Americans), or about 1,130 feet per second (340 meters per second), so it’s a little under five seconds per mile.

5

Damn, you guys type fast. I just delayed a minute or two to check that I was right about 770mph.

6

BTW: Here’s a cool calculator for theSpeed of Sound that let’s you correct for temp and humidity. (I used 21 C and 100% R.H. – because it was raining, according to the OP – to get my figures.)

7

Oh yeah, I wanted to add that the “No” in my first post was in response to the OP, not tomndebb or Q.E.D.. I may be a stickler for grammar, but what’s a few fps or mps among friends?

8

You should have taken the time to find a better source for your speed of sound. :wink: In 1986 it was recalibrated and found to be 331.29 meters per second (741.1 miles per hour) at 0° C at an air pressure of 1013.25 millibars (14.7 lb/sq ft) at sea level. (There was a lot of hoopla when an engineering or physics student rechecvked the numbers and discovered that the 1942 calculation had beenn in error.)

9

hard to believe that it took 44 years for someone to re-check that calculation.

Ficer67

10

Sorry. Cat on the keyboard is making me hit submit before he can change what I’ve typed and I’m missing some of the other posts.

I suppose that if you want to be realistic and consider real world temperatures and stuff, you can get different speeds.

Ficer67: yeah, it was a really big surprise at the time.