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Re: [Phys-L] [External] lightning strikes in slo-mo



Wonderful videos. However, an essential part of the process is not shown in the video. before the downward stroke from the cloud occurs, a small stroke starts upwed from pointed, tall objects on the ground - this is called a "dart leader". The dart leader connects with the potential gradient in the air below the cloud and a lighting stroke eventually connects with the leader. In fact, it is common for a stroke to actually go from a pointed object on the ground upwards TO the cloud. When I was working on my PhD at the University of Nevada, we took lots of film of lightning over the Sierra mountains. Little of it followed the textbook examples.


Thanks for the videos -


Bob at PC

________________________________
From: Phys-l <phys-l-bounces@mail.phys-l.org> on behalf of John Denker via Phys-l <phys-l@mail.phys-l.org>
Sent: Thursday, March 7, 2019 1:40:04 PM
To: Forum for Physics Educators
Cc: John Denker
Subject: [External] [Phys-L] lightning strikes in slo-mo

Footage of lightning strikes, showing the distinction between
leaders and the main stroke.

Shot at 28,500 frames per second, then 103,000 frames per second

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There is a lot of interesting physics involved in this.
Reference: Feynman volume II chapter 9.
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