# Question about "suction" , and overall physics, in this Whoosh Bottle Experiment

https://www.chemedx.org/blog/there-more-whoosh-bottle

So this is a pretty standard "Whoosh Bottle" experiment, but with a twist, in that he covers his hand (palm) on the bottle after the flame dies out. I understand why the bottle is squished, but what I don't understand is how the bottle got "sucked", or stuck, to his hand. What is the physics behind this suction?

From what I understand, and I could be wrong, suction is the consequence of pressure differential, whereby fluid flows (pushes) from a region with higher pressure into the region with lower pressure. How do I use this to explain the suction effect that is observed when he covers the bottle with his palm?

Surely, treating his palm as a fluid with higher pressure that is trying to flow into the bottle, hence causing the suction effect, is a little farfetched, if not outright incorrect. Is it possible that it is the atmospheric pressure that is pushing the palm inwards, hence causing the suction?

I apologize if my question sounds stupid. Please feel free to explain in as much detail as you see fit. Mathematical equations of any level, if required, would be welcome.

The bottle got squished - you said you were ok with that, due to the air pressure on the outside being greater than the air pressure inside. That pressure difference increases as the air in the bottle cools.

That same pressure difference applies to the top and bottom of the bottle, i.e. it's being pressed inwards from all sides. There is an upward force $$\Delta P \times A$$ at the bottom, but a downward force $$\Delta P \times (A - \delta A)$$ on the top of the bottle, where $$\delta A$$ is the area of the neck of the bottle covered by the demonstrators hand.

Therefore there is a net force $$\Delta P \times \delta A$$ on the bottle, upwards pressing it against his hand.

An alternative way of looking at it, following your sentence

"suction is the consequence of pressure differential, whereby fluid flows (pushes) from a region with higher pressure into the region with lower pressure."

is that there is fluid trying to push into the bottle (at the neck), but it's being blocked by his hand, it still tries to push in, but ends up pushing his down onto the neck of the bottle.

the first way of looking at it seems to explain more easily why the bottle can be lifted into the air, but maybe that's a matter of opinion...