I have a favorite glass that I take to Peets for my
morning coffee. I prefer the taste and feel of glass for a fine cappuccino (no whipped cream)
to the standard plastic lined paper cup. It is also beautiful and, in
environmentally loony San Francisco, it is a sign of an
environmentalist to bring one's own coffee cup to a coffee shop.
The glass is insulated with a hollow area between the inner cup and the outer cup. In geometric terms, it is a hollow sphere pressed into the shape of a cup without the inside touching the outside. I assume the space inside is filled with air, but it might be of a lower pressure than the outside atmosphere since it was hot when it was sealed.
Quiz: When I wash the cup in a dish pan and fill it with water, will the cup float?
Answer: Archimedes. Mass not weight is the issue. Just the glass as a lump would sink in water. This glass has been stretched into a hollow sphere and would unquestionably float. The glass, filled with water, merely turns itself over and floats pretty much like a sphere.