Re: [Phys-l] Buoyancy again

[John Denker <jsd@av8n.com>]

On 01/04/2011 04:46 PM, LaMontagne, Bob wrote:
> My question involves a blob of air in contact with an asphalt parking
> lot. That blob of air will attain a significantly higher temperature
> (and lower density) than the surrounding air. Why does it rise? It is
> in intimate contact with the asphalt and none of the denser air has
> seeped under it (or perhaps it has?)

The ambient air seeps under.

Hint:  Principle of virtual work.

This phenomenon calls into question the mantra that hot air rises.  
As a famous person pointed out:  If all of the air is hot, none of 
it rises.