For this experiment, you require a right-sized rubber ring that would fit well on the glass.
First, take one glass and drop a lighted piece of paper into it. Before the paper burns out , invert the other glass on top and put the rubber ring in between. By the time the paper has burnt out, the glasses would be joined together. Now if you pick up the top one only, the bottom glass would also come up with it. Yes, they’ve got joined-simply with air!
Did you know how??????
The oxygen present inside the glasses is used up in the burning of paper leading to decrease in air pressure. The air pressure outside is greater and acts on the glasses forcing them to stay together.
(This should be performed only under the supervision of adults)