There is a desk-top puzzle making its way around my university, sold as "Newton's Gravity Defying Puzzle". It consists of a cup with a little cylinder that sits inside. Here are some pictures:
The goal is to remove the red cylinder without moving the base or using tools. Its solution is to blow air on the cylinder, causing it to jump out out of the cup.
The explanation I heard is that you're reducing the pressure above the cylinder, which causes it to rise upwards. However, I'm less and less satisfied by that vague description the more I think about it.
Is it the tiny amount of air surrounding the cylinder inside the cup which pushes it out? If this is true, how exactly does this happen? The air is around the edges of the cylinder, and I'm having trouble envisioning how it will apply an upwards force on the cylinder. I tried to fill the gap by wrapping paper around the cylinder to test this, but found it difficult to do so without introducing too much friction.
It's worth noting that blowing works both if you direct the air straight down at the face of the cup, and if you blow from the side, directly parallel to the face. It also works with the cylinder upside-down (pointy-face down).
Another possible explanation is that pressure isn't the main mechanism here, which I would find more perplexing: if that were the case, I would think that you could make this work in a vacuum by throwing marbles at the cylinder very hard, which my intuition finds hard to believe could work. However, if I'm wrong, how would this alternative mechanism work?