Thermal energy of a substance is determined by the movement of the molecules and the potential energy of the arrangement of molecules. heat transfer will stop when thermal equilibrium is reached. it depends upon the substance how long that takes.

Why does the equilibrium position of the spring change when a mass is added to the spring? will the mass oscillate around the new equilibrium position of the spring or the previous position without a mass attached to the spring? if the equilibrium position of the spring changes by 20 cm (assuming no initial mass) when a mass is added to the spring with constant 4.9 kg/s^2, what is the mass of the object attached to the spring?