Which physical law underlies the first law of thermodynamics?

Conservation of energy

Explanation:

The first law of thermodynamics is given by :

Here,

Q is amount of heat added to the system

is change in internal energy

W is amount of work done by the system

It is clear that the energy can be neither created nor destroyed, it remains conserved. Hence, first law of thermodynamics shows that conservation of energy.      

radiation warms things up temp rises convection currents air circ windy weather

conduction, convection, radiation