A leaky bag - or is it?

How can you pierce a plastic bag full of water without spilling a single drop?

Safe­ty pre­cau­tions



  • plas­tic bag;
  • pen­cils;
  • wa­ter.

Step-by-step in­struc­tions

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 ;)

Process de­scrip­tion

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.