When a rubber sucker is pressed onto a flat glass surface, it sticks tightly on the surface. Why? You need a large force to separate it from the surface. Why?

When a rubber sucker is pressed onto a flat glass surface, it sticks t

1.	When a rubber sucker is pressed onto a flat glass surface, it sticks tightly on the surface. Why? You need a large force to separate it from the surface. Why?
Answer» When a rubber sucker is pressed onto a flat glass surface, practically all the air between the surfaces of the sucker and the glass is pushed out. The air pressure there becomes much less than the atmospheric pressure. Hence, the sucker sticks to the glass due to the external atmospheric pressure. The atmospheric pressure is about 105 Pa. It is very large. Hence, to work against it to separate the sucker from the glass, a large force is needed.