1Two things to know about air
Air pushes — and rushing air pushes less
You can't see air, but it's a crowd of tiny bits bouncing on everything. Two quick demos build the whole puzzle:
Still air pushes hard
Calm air presses from every side. The arrows are its sideways push. Left push and right push are equal, so a thing just sits there.
Fast air pushes less
When air rushes past, its sideways push shrinks. Speed it up and the side arrows get short. (Where it speeds up, it stops pressing as hard.)
2The two sides of a can
Calm outside, rushing inside
When you blow through the gap, each can suddenly has two different kinds of air on its two sides. They push against each other — and the bigger push decides which way the can moves.
Long arrows, full push
The air on the outside of the cans is still and calm. It keeps its full sideways push, pressing each can inward, toward the gap.
Short arrows, weak push
The air you blow zooms through the gap. Fast air has less sideways push left over, so it presses each can outward only weakly.
3Your turn — be the blower
Set the blow speed and watch the arrows
Move the slider to blow harder through the gap. Watch the inside (rushing) arrows shrink while the outside (calm) arrows stay long. Don't worry about the cans yet — just watch the pushes.
4Now let the cans move
Set the cans free and blow 💨
So far the cans were locked in place. Next we unlock them — but first, you have to call it. Once the air is rushing through the gap, which push wins?
Guess before you set them free
Two light cans hang with a small gap. You blow air hard, straight through the gap between them. Do they swing apart or clap together?