MLA Citation: Bloomfield, Louis A. "Question 1258"How Everything Works 14 Aug 2018. 14 Aug 2018 .
1258. Is it true that you can determine the distance of a lightning bolt by counting the second that are between the sound of the thunder and the flash of the light? I heard that every second represents one mile in distance. — LS, Los Gatos, CA
You can tell how far away a lightning flash is by counting the time separating the flash from the thunderclap. Every five seconds is about a mile. The reason that this technique works is that light and sound travel at very different speeds. The light and sound are created simultaneously, but the light travels much faster than the sound. You see the flash almost immediately after it actually occurs, but the thunderclap takes time to reach your ears. You can determine how long it takes sound to travel from the lightning bolt to your ears by counting the seconds between the flash and the thunderclap. Since it takes sound about 5 seconds to travel a mile, you can determine the distance to the lightning bolt in miles by dividing the seconds of sound delay by 5.