Re: [Phys-l] Electric Forces on Clouds

[John Denker <jsd@av8n.com>]

On 02/09/2007 03:21 PM, S. Goelzer wrote:
> A student asked a great question that I am not sure how to answer (or  
> if my interpretation of first principles are correct).
>
> "If a cloud becomes polarized and induces an opposite charge on the  
> ground then is the cloud pulled towards the ground? Do charged clouds  
> float lower?"

That's several questions all rolled together.

-- Does the electric field /pull/ on the cloud?  Sure it does.

-- But remember, force is not the same as motion.  Does the
 cloud actually /move/ in the direction of the pull?  Sometimes
 yes, sometimes no, sometimes more than 100% no.

The interesting case, and the very common case, is where the
cloud is actually moving in the direction /opposite/ to the
direction of the electrical force, such that energy is flowing
out of the cloud into the electric field.

Where do you think the atmospheric electric field comes from?
The CBs (cumulonimbus) drive the electric field.

Hint:  Feynman has a whole chapter on the subject.  It's in
volume II, but it's written at a level that a high-schooler
should be able to read ... especially a high-schooler who is
motivated enough to ask such questions.