A jar is filled to the top with water, and a piece of cardboard is slid over the opening so that there is only water in the . If the jar is now turned over, will the cardboard fall off? What will happen if there is any air in the jar?

it will all fall unless these is air

Explanation:

If you do it carefully enough, a small amount of water will pour out of the glass — that's supposed to happen. But try not to let any air bubbles get into the glass. Finally, slowly remove the hand holding the cardboard in place.