https://what-if.xkcd.com/6/ has been mentioned here before, but I'm questioning whether or not the glass cup with the bottom half as a vacuum would rise at all.
To start with, a vacuum exerts no force. Any perceived "sucking" is actually external pressure pushing into the vacuum. So the only force that could be lifting the glass would be buoyancy of the air around the cup.
Let's ballpark it with a drinking cup that can hold about 500ml. If we consider the cup as an open-top cylinder, an internal radius of 3.8 cm and height of 11 cm gets us a 499ml volume, and the internal surface area is 308 cm^2. Based on a quick Google search, glass is about 2000x more dense than air, so in order for the glass to rise it would need to displace 2000x as much air as there is glass. That suggests that if the glass was sealed (by a weightless forcefield at the top) and was completely empty instead of having some water in it, the total volume of glass would have to be less than 0.5ml, resulting in an average width of 0.016mm. That's thinner than a human hair.
Given that glass cups are significantly thicker than human hair1, is there any truth to the conclusions of that "What If?" Is there some effect that I've misunderstood or underestimated that significantly changes the situation? Or should we conclude, like https://physics.stackexchange.com/a/33642/79374 did with the other vacuum cup, that Randall Munroe either miscalculated or was greatly exaggerating?
1 Citation needed