Materials

Structure and properties

Let's take a close up look at the fibers of a newspaper. We would see that the fibers in this newspaper are long, thin strands that all line up to go in the same direction. This means that if you tear the newspaper one way (vertically in this case), you would face little difficulty. If, however, you were to tear it the other way, you may find it considerably harder to tear in a straight line. This is because when you tear the paper in the first direction, all you're actually doing is separating the fibers. Tear the paper in the other direction, however, and you will find it harder, because you actually have to break the physical fibers of the paper. Imagine the situation as a bunch of pencils, all lined up in a row. Separating them one way is easy just move about half the pencils on way, and the other half the other. That's not an issue. Try and separate the pencils the other way, and you will find it considerable harder - you would actually have to break the pencils in half to move them in this fashion.

A good example of this effect in action is in the making of higher quality paper cups. A company is considering two plastic structures that they can use to make their cups:
A you can see, the molecules in the first cups are arranged in a way similar to newspaper fibers - all in one direction. When you try and tear the cups therefore, it's relatively easy in one direction (separating the molecules) and a lot harder to tear if you're going in the perpendicular direction: 
Let's have a quick look at the structure of the other considered plastic that could be used in this process (below). As you can see, the structure of this plastic is molecules that line up all in the same way vertically, and in the same way horizontally. This means that whichever way you try and tear the cup, you will have to break fibers to do so. This means that the cup is difficult to tear in either direction, is longer lsting and is therefore said to be of a higher quality.