Wednesday, 21 July 2010

Counting between lightning and thunder

It's true, you can count between lightning and thunder. However, as you can see below it's 5 seconds for every mile - I was counting 1 second per mile.

From the BBC Weather Centre:

"Air around the discharge channel is heated to about 30,000 C (55,000 F). The sound of thunder is made by heated air expanding very rapidly and causing soundwaves. Thunder rumbles because you get soundwaves coming from different parts of the storm. The speed of sound (760 mph, 1224 km/h) is very much less than the speed of light (186,000 mp/s, 300,000 km/s). So you see a lightning flash almost immediately it happens while the sound can take several seconds to reach an observer. If you count the gap between the lightning and the thunder, you can tell how far away the storm is. For every kilometre count 3 seconds, for every mile count 5 seconds. So if you count 15 seconds, the storm is 5 km or 3 m away from where you are."

1 comment:

  1. I had always thought of it as 1 second per mile too.