What happens when you blow really hard between two hanging cans?
Two little cans are hanging here, with a tiny gap in between… Now take a big breath, and blow right down the middle, as hard as you can! What do you think the cans will do? Will they swing apart… or come together? Ready to guess?
After you watchWhat happens when you blow really hard between two hanging cans?
The short answer
When you blow hard between two hanging cans, they swing together, not apart. Fast-moving air is a gentle pusher, so the calm air on the outside pushes harder and nudges the cans toward each other.
Try this next
- What if you blow on the outside of just one can? Aim your breath past one can's outer side and guess first — which way does it swing? Watch where the soft-push air pulls it toward.
- What if the cans hang farther apart? Slide them wider, take the same big breath, and predict: do they still clap together, or is the gap too big now?
The whole story
How it works
Air is always gently pushing on everything from every side. Usually each can gets the same push on both sides, so it just hangs still. When you blow fast air through the gap, that rushing air pushes softer than the calm air. Now the calm air on the outside pushes harder than the rushing air in the middle, so it nudges the two cans together.
What people get wrong
Most kids guess the blowing air will shove the cans apart, like wind pushing a swing. But fast air is a soft pusher, not a hard one. Nothing sucks the cans in either — the calm air outside simply wins and pushes them together.
The catch
The cans only come together while the air keeps rushing. Stop blowing, and both sides go calm and even again, so the cans drift back apart. It is not magic glue — it needs the moving air to keep working.
Questions kids ask
Does the blowing air push the cans apart?
No — that is the surprise! Fast air is a soft pusher. The calm air on the outside pushes harder, so the cans come together while you blow.
Is something sucking the cans in?
No sucking and no pulling. The calm air outside is just pushing harder than the rushing air in the middle, so it nudges the cans together.
What happens when I stop blowing?
The cans drift back apart. The rushing air made the soft push, so once the air stops, both sides feel the same calm push again and the cans hang still.
Talk about it
- Before we blow, guess together: will the cans fly apart or come together?
- If nothing is pulling the cans, what do you think is doing the pushing?
- Where have you felt this — does the shower curtain ever stick to your legs when the water is on?
For grown-ups
This is Bernoulli's principle in kid form: faster-moving air has lower static pressure. Blowing through the gap speeds up the air there and lowers its pressure, so the higher-pressure calm air outside provides a net inward push. Nothing is 'sucked' — there is no pull, only an unbalanced push from the calmer, higher-pressure side, and it lasts only while the air is moving.
Keep going
What else makes you wonder?
- What if you blow even harder — do the cans come together even faster?
- If air is always pushing on you from every side, why can't you feel it?
- What else at home sneaks toward something when air or water rushes past?