The principle of paper bags mainly includes the following aspects:
Air pressure balance: The air inside and outside the paper bag will ventilate each other through the tiny pores of the paper bag, so that the pressure inside and outside the paper bag is basically balanced. In this way, objects placed in the paper bag (such as pens) are not easily squeezed out by external forces.
Friction: The friction between the inner wall of the paper bag and the surface of the object helps to prevent the object from sliding out. Paper bags usually have a certain coefficient of friction. When the surface of the object rubs against the inner wall of the paper bag, the friction will offset the tendency of the object to slide.
Fixed shape of paper bags: Paper bags are usually made in a folded form and have a certain fixed shape. This shape makes the paper bag have a certain pressure resistance. Under the action of external pressure, the paper bag can maintain a certain shape, making it more difficult for the object to be squeezed out.
