The card isn't holding the water in. The sky is.

We live at the bottom of a massive ocean of air — the atmosphere — and it pushes down on everything around us with an enormous force called atmospheric pressure. Not just downward either. 

Sideways. Upward. In every direction, all the time.

When you flip the cup, the water pushes down on the card with its weight. But the atmosphere pushes up with far, far more force. The water doesn't stand a chance of falling — it's being held in place by the entire weight of the sky above you.

Did you notice the card barely bends? That's the pressure being perfectly even — no gaps for air to sneak in and break the seal. Did you also notice that tilting it sideways still works? The atmosphere doesn't care which direction it's pushing. It wins every time.

That same invisible force is what makes straws work, what holds suction cups to walls, and what lets you breathe right now. 

You can feel it doing something equally surprising in [The Chatterbox Tube]— where atmospheric pressure inflates an entire tube from a single breath — and watch it crush a sealed container in [Feed the Monster].

You're surrounded by it every moment. You just can't feel it because it's been pushing on you your whole life.

But here's the real question — how much does the atmosphere actually weigh? The answer will make your brain hurt. And can you do this trick with no card at all? 

Find out in The Crazy Scientist Lab!