I was able to chop the ruler in two because of air pressure. When I spread out the newspaper on top of the ruler, I basically created a large suction cup because I’ve preventing air from flowing underneath. When I strike the ruler, it tries to lift up against the newspaper, but because the air can’t flow very quickly into the space between the table and the newspaper, most of it simply pushes down on the newspaper (and the ruler).
Since I had 8 inches of ruler covered by the newspaper. And one inch wide, that would mean that the area is 8 square inches. Remember that the 80 mile column of air above us presses down at 14.7 pounds per square inch. That means my ruler had 120 pounds of pressure holding it down while I chopped
The point is that when the ruler tries to lift off of the table, it has to push against all 120 of those pounds.