Estimating the Distance to LightningDate: 08/16/99 at 23:43:15 From: nick Subject: Calculating the distance of lightning from the thunder Hello Dr. Math: I have been having discussions with friends about how far away lightning is, based on when we hear the thunder. I've explained that since sound travels about 1122 feet per second through air, and there are 5280 feet per mile, for every 4.7 seconds between the lightning and the thunder the lightning is one mile away. Can you explain it any better? Thanks. Date: 08/17/99 at 13:11:46 From: Doctor Peterson Subject: Re: Calculating the distance of lightning from the thunder Hi, Nick. You've got it right. Let's see if I can give a fuller explanation. When lightning strikes, it produces light and sound. The light travels fast enough that we can think of it as instantaneous over distances of a few miles. So when we see the lightning, we are seeing it at the time it actually struck. The sound travels at about 1/5 mile per second (to keep the numbers simple). So for every mile the sound has to travel, it will take about 5 seconds to reach us. If we divide the time between the light (the time of the flash) and the sound (the time when we hear the thunder) by 5, we get the distance in miles. Or you can say we're multiplying the number of seconds by 1/5 to get the number of miles the sound traveled in that time: mile distance = 1/5 ---- * time sec - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
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