1Two things to know about air
Air pushes on surfaces
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.
Pressure can be different
In a lower-pressure region, the sideways push is smaller. Shorter arrows show its weaker sideways push. Speed alone does not tell us the pressure in every airflow.
2Two regions of our test
Outside air and the narrow gap
The test has air outside the cans and air between them. Each surface feels a push from the air touching it. We will change the gap condition after your prediction.
The surrounding air
The outside air presses on the outer surfaces. These surroundings stay the same during the test.
A separate flow region
The gap touches the inner surfaces. Flow and geometry can change its pressure; fast air does not automatically mean low pressure everywhere.
3Your turn — balance two pushes
Change two equal pressures together
This block has equal pressure on both sides. Change both together. Longer arrows mean larger forces, but the pushes still balance. The can test changes only one region.
4Now let the cans move
Set the cans free and change the gap pressure
Now apply the two-sided push idea to a new arrangement. In this idealized test, the gap pressure is reduced while outside pressure stays the same. Predict the can motion before you change it.
Guess before you set them free
Two cans hang with a gap. Gap pressure becomes lower than outside pressure. Do the cans move apart or together?