Using the energy gradient color map, each seperate books exhibited low energy values simply due to the fact there was no transfer of energy between each book when that were seperate(not touching one another). Hence, each book maintained the energy level of the environment.
After the books were stacked together, the books at the bottom experiences greater pressure due to the load or weight of the books above, leading greater level of energy maintained by the books below.
The books on top still maintains the same level of energy has that of the environment as they do not experience additional pressure.
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