A leaky bag - or is it?
How can you pierce a plastic bag full of water without spilling a single drop?
- plastic bag;
Pour some water into a plastic bag, then pierce the bag with a sharp pencil. Push the pencil all the way through the bag to leave one end sticking out on either side. The water doesn't spill out! We dare you to try it over a friend's head ;)
Plastic bags are made of a polymer called polyethylene. A polymer consists of long chains of identical molecular units. These chains can branch and intertwine, making the material even stronger and more elastic. When we pierce the bag, the pencil's tip breaks these intermolecular bonds. As it continues further through the hole, the pencil pushes the chains apart, but the connections between the chains resist this. Therefore, the deformation of the chains leads to the appearance of forces tightly stretching the polyethylene around the pencil.