# Speed for lightning and thunder

1. Mar 5, 2006

### emma123

i don't understand how you can estimate how far the lightning flash is from you by counting the seconds betw the flash and thunder, then divide by three to result in the distance in kilometers. can someone please explain where does the logic that resulted in this rule? i don't understand why it is this. thanx

2. Mar 5, 2006

### Staff: Mentor

Well, it's all about the speed of sound - speed times time equals distance.

3. Mar 5, 2006

### emma123

i still don't understand. is it that for speed *time = distance. that for the speed of sound is approx. 340m/s so when you divide 1000m by 340m/s you get about 3. therefore you need to divide by 3 to get the distance. am i off track?

4. Mar 6, 2006

### Intuitive

The http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html#c5"
changes with Atmospheric Density and Temperature.

Ideal Speed of Sound in Air.
Approximately 331 Meters per Second for Sound in Air.
Approximately 1,085.958 feet per Second for Sound in Air.
Approximately 740.4259 miles per Hour for Sound in Air.
Approximeately 2,174.302 Miles Per Hour for Sound in Helium.
(Compare to Speed of Light 670,616,640 Miles Per Hour in a Vacuum)
Approximately 12.34043 Miles per Minute for Sound in Air.
Approximately 0.2056739 Miles per Second Sound in Air.

So if Sound travels 1085.958 feet per Second in Air then it would take Approximately 4.5 Seconds for Sound to travel 1 Mile, This should change with Elevation(Atmospheric Density) and Temperature(Tc).

Last edited by a moderator: Apr 22, 2017
5. Mar 6, 2006

### Integral

Staff Emeritus
Keep in mind that the speed of sound in air is 330m/s at 0C. at thunderstorm temps it is more like 350m/s

6. Mar 6, 2006

### Galileo

Uhm. Yeah, so if you wait one second, the sound will have traveled about 340 m, which is about 1/3 of a kilometer. That's all there is to it.

7. Mar 6, 2006

### Intuitive

It would be cool to have a little hand held size unit that detects a Lightning Flash and then listens for the Thunder Clap of that Lightning and then calculates the distance to the Lightning Bolt Automatically on a Digital read out, It sounds like fun.

8. Mar 6, 2006

### Staff: Mentor

3/3=1. 1 km. I'm not sure what the problem is here...

9. Mar 6, 2006

### DaveC426913

I have one. But it's not handheld, I keep it balanced between my shoulders. :rofl:

Once it detects a flash, it begins counting "one one thousand, two one thousand...". If it detects a rumble after 3 seconds, then the bolt is 1 km away; for each 3 seconds beyond that, the bolt is +1km away. If you're American it's 5 seconds per mile.

Last edited: Mar 6, 2006
10. Mar 6, 2006

### DaveC426913

What is kind of cool is that you can tell (to some extent) the direction of the bolt by listening to the quality of the sound. This only works for bolts that are close-by though, so that the rumble isn't echoed and attenuated by distance.

In a nutshell, a short rumble comes from a bolt that is traveling with "proper motion" (i.e. across the sky relative to you), whereas a long rumble is travelling toward you or away from you.

You know, you could get a second buddy who lives a few km away, and get on the phone with a stopwatch and map lightning bolts...