Books are printed as varying quadrilateral shapes, and are placed onto bookshelves that are designed to have three walls and an open face to display the book spines. Stone tablets, illuminated manuscripts, bound books, etc. are widely made in rectangular shapes, and I have to agree that this makes a lot of sense to keep it that way.
Accordingly, for my next physical experiment, I decided to focus on form and weight. I wanted to evaluate the opposing options through the lens of these two categories. I took a floss dispenser with a flat bottom face and rounded edges to explain that in order for books to stand upright, they must have enough surface area at the bottom to sustain itself. As soon as I attempted to lean the case on the rounded parts, it would immediately slip and fall flat on its side.
I then realized that if the case were placed between two flat surfaces, it would still hold up because of the friction and weight placed on either side of the object. When it was placed between two books, it held just perfectly. However, when I tried to lean it on one rectangular block, it continued to slip and fall. In order for it to be stable, it needed to have support on either sides. In the images that display the case standing on the curved edges, leaning against the books, I had to muster up all my patience to try and set it to stay that way. The weight needed to be balanced, considering its form, because the curved edges did not provide enough surface area for it to rest securely.
In the end, I concluded that it really does make sense for a books to be manufactured in the shapes that they are. The traditional standard bookshelf designs, therefore, are mostly recognized for function over their form.