Here's how it works:
* Paper is made from fibers: Paper is made from wood pulp, which is essentially a tangle of long, thin fibers.
* The fibers are aligned: During the papermaking process, these fibers are aligned in a specific direction, creating a grain. This alignment is usually determined by the direction of the paper machine's rollers.
* The grain determines the strength: The fibers are stronger when pulled in the direction of the grain (with the fibers) and weaker when pulled perpendicular to the grain (across the fibers).
* Clean rip: When you rip a page of newspaper with the grain, you're pulling the fibers apart in their strong direction. This leads to a clean tear.
* Ragged rip: When you rip against the grain, you're breaking the fibers, resulting in a more jagged, ragged tear.
Think of it like this: Imagine a chain made of links. It's easy to pull the chain apart lengthwise, but much harder to break it by pulling across the links.
This grain is also why you'll see a newspaper roll up more easily in one direction than the other. You're rolling with the grain when it rolls smoothly!