“P + ½ ρ.v2 is a constant” – Daniel Bernoulli
You’ll find this little equation inside things all over the place. And one of the far-from-obvious results is that blowing can suck.
You might have seen a little hovercraft created from a balloon and a CD. They’re simple enough to make: you take a CD, stick a stub of a plastic tube on it, on the side with the ridge for the balloon. Inflate a balloon and hold the neck while you attach it to the CD. Let go of the balloon neck, and air will whoosh out from the middle and it’ll hover and glide beautifully across a smooth table.
But now try this. Check your ceiling is smooth, then try your little hovercraft upside down on the ceiling. That’s nuts, right? It’ll blow itself away from the ceiling and fall down to the floor quicker than if you just let it go under gravity, right? Nope. It’ll suck itself up but then...