Unsolved
As the title is observed, it is found that the bottoms of many beverage and drinking water bottles are concave.
Why is it not flat?
At first I thought it was to pack a little less content, but most of it was originally not full, and the bottom of the bottle was not large in volume and the liquid level would not rise much because of this. It is also speculated that it is to increase the friction of the bottom of the bottle, but the pattern can also be achieved why all the depressions are selected. Or is it for the convenience of bottle blowing (I don't know much about professional manufacturing process)?
