[paul.fr]

It is often said that you can tell how far off a thunder storm is by counting the seconds between the flash of lightening and the sound of thunder.

But how true is this? Does anyone know?

[lightarrow]

It is often said that you can tell how far off a thunder storm is by counting the seconds between the flash of lightening and the sound of thunder.
But how true is this? Does anyone know?

You see the flash and you start your chronometer. When you hear the bang, you stop it.
Seconds*340 = distance in metres (sound's speed in the air = 340 m/s). Where is the problem?

[daveshorts]

It is very true, it works because light moves so fast that over the sort of distances yo ucan hear thunder it is essentially instant, but sound travels 1km in about 3 seconds, so if you time the difference in time between when you see the lightning and when you hear the sound it makes from this you know how long the sound took to get to you and therefore how far away the lightning was.

[elegantlywasted]

Wait a minute... 3 seconds is equal to 1km? I worked outdoors on a farm last summer and we weren't allowed to come inside unless there was a 5 second delay... I knew they were hoping we'd fry in those greenhouses

[FreeThinker]

It's 5 seconds per mile.

[daveshorts]

Sounds about right