The way paper tears is related directly to how it is made. Most paper is made from wood fibers. Logs are chopped into wood chips, mixed with water and chemicals, and run through a process that separates the wood fibers. The soupy mush that results is called pulp. The pulp is pressed onto a mesh conveyor belt that squeezes the water out. As the pulp moves along the belt, the wood fibers line up in the direction of the belt’s travel. This alignment of the fibers on the belt gives the paper a grain. This grain is what causes the paper to tear straighter one way than the other. When paper is ripped with the grain, the tear goes with the direction of the fibers, and is fairly straight. When you tear the paper across the grain,the tear tends to wander as it works against the direction of the fibers.

【生词注释】
tear n. 撕
chop v.砍，劈
mush n.软糊状的东西
pulp n. 纸浆
alignment n.排列
grain n. 成粒状

【参考译文】
撕纸的方式直接同纸张的制作紧密联系。大多数纸都是由木纤维制成的。木头被砍成木片，同水和化学物质一起搅拌，经过一种流程将木纤维分开。产生的浆糊状的物质叫做“纸浆”。 纸浆再在网状的传送带上挤压，将水挤出来。随着纸张在传送带上移动，木纤维会向着传送带的方向排列。纤维在传送带上的排列会使纸张成粒状。这种粒状会使纸张在撕裂时在一个方向比另一个方向撕得直。当纸张顺着粒状撕时，撕的方向和木纤维的方向相同，撕得就会很直。当你从粒状中间撕纸时，因为撕的方向和木纤维方向相反，撕得就会弯曲些。