>>The top of the can is then added. This is carefully engineered: it is made from aluminum, but it has to be thicker and stronger to withstand the pressure of the carbon dioxide gas.<<
Eh? The pressure is greater at the top of the can?
Eh? The pressure is greater at the top of the can?
Another interesting fact is the can is narrower at the top to reduce the size of the lid, saving cost and mass.
Lots of details and photos on aluminum cans at http://www.chymist.com/Aluminum%20can.pdf so check it out.
There's an interesting Slate article[1] about the complexity of what appears to be a such a simple feature; in order to achieve the force necessary to rupture the can opening, the tab pivot transitions between a first and second class lever. There's a good video somewhere showing the principles, but I can't seem to find it.
Returning to the 'pressure' argument, recall that most drinks cans have a domed bottom which provides comparatively greater strength than the flatter top.
[1] http://www.slate.com/articles/life/design/2012/09/can_tabs_h...
Though I do know with most certainty that if placed in a freezer and left then it will expand at the top and the bottom and mostly rupture a bit around the ring pull tab in the process.
Pressure inside an enclosed volume is equal everywhere.
Smaller is about cost. They save a bit (say $3 per 1,000 as per link I posted elsewhere) by making the top 1/4 inch smaller.
Over 70 million cans a day that's some cash.