You didn't inflate that tube. The room did.

When you blow across the opening rather than into it, your breath creates a fast-moving stream of air right at the mouth. And fast-moving air has a surprising property: it has lower pressure than the still air around it. Scientists call this Bernoulli's Principle.

That low-pressure zone acts like an invisible pump. The higher-pressure air from the rest of the room rushes in to fill it — flooding through the opening, joining your breath, and blasting down the length of the tube in one smooth surge. You supplied the trigger. 

The atmosphere did the heavy lifting.

Blow directly into the tube and you're limited to what your own lungs can push — one small lungful at a time. That's why it takes so many more breaths and so much more effort to achieve the same result.

Did you notice the tube inflates in one continuous rush rather than filling gradually? That's the atmospheric pressure flooding in all at once the moment the low-pressure zone opens the door.

Bernoulli's Principle is at work all around you: it's how aeroplane wings generate lift, how a curveball curves away from the bat, and why your shower curtain swings toward you when the water runs. 

You can see the same principle hold a ball suspended against gravity in [The Impossible Blow], and feel the full force of atmospheric pressure doing something equally surprising in [The Magic Water Cup].

How far from the opening can you hold your mouth and still trigger the atmospheric pump with a single breath? 

Find out in The Crazy Scientist Lab.