Peter,

Your understanding of physics is slightly incorrect.

> The pot needs to be lightweight (less mass to heat), except
> that the bottom has to be flat, and as good a heat conductor
> as possible.

Heat conduction is directly related to thickness and mass. Just as in
electrical wires (the thicker the wire, the more electrons it can
carry), the thicker and heavier the pot, the better it will conduct heat.

Since metals used for cooking are all 'good conductors", they will
conduct the heat quickly to the material inside. In addition, since
metals don't hold heat well, there is little heat loss due to the mass.

Note that silver and copper are the best conductors, as they are very
dense, compared to aluminum, the third best conductor.

You are correct in that the flatter the bottom, the better it is for use
with a flattop cooking unit.

Colin