Thermal mass in passive solar buildings is usually dense material such as brick or concrete masonry, but can also be tile, water, phase change materials, etc. Generally, the thicker the wall, the less the indoor temperature fluctuates. There are four laws, of which the first and second are most often discussed. The second law states that all physical processes, natural and technological, proceed in such a way that the availability of the energy involved decreases. That is, when we consume energy it is not energy itself that is consumed, but its availability for doing useful WORK .
All physical processes proceed in such a way that the entropy of the universe increases.
Entropy is a well defined measure of disorder that can be shown to be a measure of unavailability of energy. So, once coal or oil is combusted for work it is physically impossible to reassemble the molecules to perform work again. The tendency of heated liquids to rise. Circulation of the collection fluid through the storage loop is provided solely by the temperature and density difference between the hot and cold fluids. Any force that acts to produce rotation.