mm wrote:
In high school physics, the three methods of heat dispersal were
presented as conduction, radiation, and convection?

Is that all there is? Is diffusion a fourth or is it subsumed by
convection?

Ah, you have forgotten the frequently seen fourth form, which is
wrapping the hot thing up in a towel and running with it over to
somewhere else where you drop it off. It can move a lot of heat very
effectively.


I could be wrong but:
Conduction seems to be limited to within a solid, or from the surface
of a solid to that part of a liquid or gas in contact with the solid.

ICBWB:
Convection seems to be limited to liquids and gases.

And ICBWB: radiation seems to be limited to from a solid or maybe a
liquid through a gas to another solid or maybe a liquid.

As to convection, it was always described and seems to be limited to
broad currents, such as hot air rising and cold air sinking, but is
that all that happens? In, say, a room with moderate cooling in the
summer or moderate heating in the winter, while in general the hot air
rises, doesn't the random motion of some of the hot air cause it to go
downward and to mix with the cooler air below it? Is this radiation?
Is it still convection? Or is it diffusion and for reasons of
definition, not one of the other three?