Can't tear something into three pieces

  • Thread starter Thread starter OranL
  • Start date Start date
AI Thread Summary
The discussion explores the physical principles behind why a piece of paper typically cannot be torn into three pieces by pulling on both sides. It highlights that the stress concentration near a crack tip influences crack propagation, which is relevant in material science. An example is given where adding weight, like a coin, to the center of the paper can allow it to be torn into three pieces due to increased inertia. The lightness of the paper's center piece usually causes it to move with one side, preventing a clean three-way tear. Ultimately, the interaction of forces and material properties determines the tearing behavior.
OranL
Messages
2
Reaction score
0
Does anyone know what physical principle theoretically prevents something from being torn into three pieces from two forces being applied? (E.g. pulling on both sides of a piece of paper will never tear it into three pieces.)
 
Physics news on Phys.org
Yes, but breaking a piece of spagahetti by bending it will usually result in three pieces (I think Feynman describes this), so your assumption is wrong.

There's some work out there on crack formation and propogation, the main result is that the stress field is locally concentrated near the crack tip, and this localizes the crack by relaxing the stress away from the crack tip.
 
See http://www.exn.ca/Stories/1998/05/06/54.asp (Discovery Channel): :smile:
If you were to tape a coin to the middle piece of paper, that would dramatically increase its inertia. It is then it is a fairly simple matter to tear the paper into three pieces. Pull sharply on the two outside edges and both outside pieces split away, because the inertia of the heavy middle piece keeps it stationary while the outside pieces tear off.
This web-page also explains why you can't do it for plain paper:
No matter how small the last remaining vestiges of paper are at the bottom of the tears, one will always be stronger than the other and will remain intact while the other side tears apart. What makes this work, however, is that the centre piece of paper is extremely light and thus has little inertia. It simply tags along with one side or another.
 
So I know that electrons are fundamental, there's no 'material' that makes them up, it's like talking about a colour itself rather than a car or a flower. Now protons and neutrons and quarks and whatever other stuff is there fundamentally, I want someone to kind of teach me these, I have a lot of questions that books might not give the answer in the way I understand. Thanks

Similar threads

Back
Top