本篇文章主要讲的是颗粒物质可以阻碍导弹。这些颗粒物质比如湿润的沙子像固体，而你把它拿在手里就又变成了流动的。科学家就这一现象解释一些现象。下面前程百利小编带大家一块看一下这篇托福听力背景材料中出现的生词，希望能给正在备考托福听力的同学带来帮助。
·Ever run along wet sand, and it hardens up (使坚硬)almost like concrete(混凝土) under your feet? But pick up that same sand and it drizzles(毛毛细雨般) through your fingers? "So that's the essence of (真髓)why granular materials(颗粒物质) are interesting...” Yale physicist Abe Clark. “…sometimes they can behave like solids(固体)." And other times like fluids(流体). Understanding the transitions(过渡时期) between liquid and solid, "that's really nontrivial(非凡的)."
Grains—of sand or otherwise—are Clark’s specialty(专业). He and his colleagues recently investigated(研究) how a bucket (桶)of beads(玻璃粉) responds when another object falls into them. It's analogous to (与什么类比)dropping a stone on sand, and then observing how the stone's force transfers(转移到) to the grains. "The top grain is contacted by the intruder|(侵入者), and then it tells a friend, and it tells a friend and so forth, and it moves along(往里走) a little chain. So what this looks like is basically little lightning bolts(闪电球) of force shooting off (发射)the intruder(侵入者)."
But the faster that impact gets—think meteor(流星) or missile (导弹)strike—the more extensive that chain-like (链状)network between the grains(谷粒) becomes, meaning the grains behave more like a solid. Which in some cases made the intruding(挤硬) projectiles (落弹数)bounce(跳) right off.
The work was funded in part by the Defense Threat Reduction Agency, part of the DoD, so of course some of the applications(应用) are military. Granular materials(颗粒材料) might be the perfect thing to thwart (挫败)a missile attack, for example. And on a smaller scale, "well if I was gonna go build sandbags for the military I'd tell them to use little rubber(涂橡胶于) pellets(芯块) to fill their sandbags with, instead of sand." Because he says rubber beads (玻璃粉)would create a stronger, longer-lasting repellent(防护剂) force against bullets. But remember, Abe and his colleagues are physicists. "I've seen a couple crazy blogs or something saying, you know, 'scientists are building bunker(沙坑) busters'(堵口) sorts of, something like that, so no, we're definitely not doing anything like that." After all, that would be a task for engineers.
疑难词汇：
Thwart vt. 挫败;反对;阻碍;横过adj. 横放的;固执的n. 划手座;独木舟的横梁
adv. 横过prep. 横过
Granular adj. 颗粒的;粒状的
Drizzle vi. 下毛毛雨vt. 下毛毛雨n. 细雨，毛毛雨
Nontrivial adj. 非平凡的
Analogous adj. 类似的;[昆] 同功的;可比拟的
Intruder n. 侵入者;干扰者;妨碍者
Bolt n. 螺栓，螺钉;闪电，雷电;门闩;弩箭vt. 筛选;囫囵吞下;(把门、窗等)闩上;突然说出，脱口说出vi. (门窗等)闩上，拴住;冲出，跳出;(马等的)脱缰;囫囵吞下
adv. 突然地;像箭似地;直立地
projectiles n. 落弹数(projectile的复数形式)
pellet n. 小球;[军] 小子弹(枪用)vt. 将…制成丸状;用子弹打;用小球扔
bead n. 珠子;滴;念珠vi. 形成珠状，起泡vt. 用珠装饰;使成串珠状
repellent adj. 排斥的;防水的;弹回的;令人讨厌的n. 防护剂;防水布;排斥力
bunker n. 沙坑;煤仓;燃料库vt. 使陷入困境;把球击入沙坑
buster n. 起破坏，制止作用的人或物;庞然大物;非凡的人或物;小鬼，小家伙;茁壮的孩子
好了，以上就是前程百利小编为大家整理的“从托福听力背景材料中学单词—沙子是固体还是液体? ”这篇托福听力背景材料中的疑难词汇，希望在备考的路上助大家一臂之力。最后，小编祝大家在托福考试中取得好成绩！
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