Question

Describe an experiment to demonstrate that air exerts pressure.

Answer 1

Air exerts pressure and this can be demonstrated by this experiment.

Take a glass tumbler. Fill it to the brim with water, with water overflowing the rim of the tumbler. Cover it with a piece of cardboard. Press the cardboard so that it touches the rim of the tumbler at all points. This will ensure that no air is left inside.
With the hand on the cardboard, invert the tumbler gently and remove the hand. Both cardboard and water shall not fall. This shows that air exerts pressure on the lower surface of the cardboard in the upward as shown in the figure. The upward thrust acting on the cardboard due to air pressure supports the combined weight of cardboard and water in the tumbler.
So, this shows that air exerts pressure.