Question

Place a piece of cardboard on the mouth of a glass filled completely with water holding the cardboard firmly in place with one hand invert the glass quickly. Take your hand away from the cardboard. What do you see?

Answer 1

Answer:

the cardboard doesnt falls

Explanation:

its sticks to the glass by inverting it quickly

Answer 2

To show the presence of atmospheric pressure, you need a glass tumbler, stiff cardboard and  water. Take the tumbler and fill it with water such that it is full till the brim. Cover it with a  cardboard piece. Then place your hand over the cardboard piece on the tumbler and quickly invert  it. Now, slowly, remove your hand whie supporting the cardboard piece. It is observed that the  cardboard piece does not fall. This proves that there is atmospheric pressure that provides enough  force to support the weight of the water in the tumbler.