Without the swirl, the water and air fight each other. With it, they share the road perfectly.

Here's the problem. As water tries to fall down through the neck, air needs to push up to replace it. Same hole. Two things trying to use it at once. That's why, without the vortex, you get that slow, glugging, stop-start mess.

Give it a swirl and everything changes. Water spirals down around the outside. Air travels smoothly up through the centre. No fighting. No glugging. Just a beautiful, efficient vortex — the same invisible engineering that atmospheric pressure uses to move water in [The Magic Water Cup], except here it's the spin doing the work rather than the air pushing up from below.

Did you notice how much faster it drains when the vortex is going? That's not a coincidence — the vortex is solving a physics problem in real time, right in your hands.

Did you also spot the hollow tunnel in the very centre of the spinning water? That's the air highway. Look closely next time — it's one of the coolest things you'll ever see in a bottle.

Nature uses this trick everywhere — from your bathroom drain to massive ocean whirlpools to the eye of a real cyclone. Always the same solution. Always that hollow centre. You can see the same spinning energy in water explored further in [Ocean Energy in a Bottle].

But here's the big question — do tornadoes and whirlpools spin in different directions on opposite sides of the world? And does your experiment follow the same rule? 

Find out in The Crazy Scientist Lab!