Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: paul.fr on 08/03/2007 19:19:35

Title: The sound of Thunder
Post by: paul.fr on 08/03/2007 19:19:35

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?

Title: The sound of Thunder
Post by: lightarrow on 08/03/2007 19:35:11

Quote from: paul.fr on 08/03/2007 19:19:35

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?

Title: The sound of Thunder
Post by: daveshorts on 09/03/2007 10:11:57

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.

Title: The sound of Thunder
Post by: elegantlywasted on 09/03/2007 12:59:47

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

Title: The sound of Thunder
Post by: FreeThinker on 13/03/2007 16:18:26

It's 5 seconds per mile.

Title: The sound of Thunder
Post by: daveshorts on 14/03/2007 16:36:09

Sounds about right