英语听力文摘 English Digest 582、保鲜膜的秘密！

 　　Why Does Plastic Wrap Cling To Itself?

 

　　What makes kitchen plastic wrap cling so maddeningly to itself, and so conveniently to the sides of bowls and plates?

 

　　Plastic wrap clings for two reasons: it’s elastic¹ and it’s sticky. That probably seems pretty obvious, but let’s explore the chemistry beneath the elasticity² and stickiness of plastic wrap.

 

　　Plastic wrap is elastic because of its molecular³ structure. A molecule⁴ of plastic is incredibly long and coiled up like a spring. When you stretch out a piece of plastic wrap, you uncoil these long molecules⁵.

 

　　Like a spring, the stretched molecules tend to spring back, perhaps tucking under the rim⁶ of the bowl you just covered! Over time, certain types of plastic wrap lose some of their elasticity, which could explain why that dish you wrapped tightly may loosen up after a day or two.

 

　　Now that you know the secret to plastic wrap’s elasticity, let’s explore why it’s sticky.

 

　　Most thin plastic films easily pick up a static electric charge by friction⁷. In other words, plastic wrap is static electricity waiting to happen. As you pull the plastic wrap from the roll, or as it brushes against your sleeve, the friction could cause electrons to be displaced onto one area of the plastic, giving it a negative charge.

 

　　The surface that lost the electrons would then have a positive charge. Since opposites attract, the plastic wrap and any oppositely charged surface, whether that’s the plate of food, your sleeve, or even another part of the plastic wrap itself, will cling to each other by electrical attraction.

 

 

 

 

　　保鲜膜的秘密

 

　　厨房保鲜膜为何能自我粘附，并且能轻易地贴合于碗盘的边缘？

 

　　保鲜膜可粘附有两大原因：它具有弹性和粘性。这看起来似乎颇为明显，但还是让我们探究深藏于保鲜膜弹性及粘性下的化学原理。

 

　　保鲜膜的弹性取决于它本身的分子结构。塑料的一个分子极长且像弹簧般蜷曲。当你将一张保鲜膜伸展开时，同时也将长长的分子拉伸开来。

 

　　保鲜膜被伸展后会像弹簧般回缩，它可能刚好紧贴在你刚覆盖的碗边。有些品种的保鲜膜会随时间而逐渐失去弹性。这也就能解释为何之前紧贴在碗边的保鲜膜会在一两天后松开。

 

　　既然有关保鲜膜弹性的秘密已揭开，那现在就来探究下为何保鲜膜会具有粘性。

 

　　大多数保鲜薄膜可通过摩擦轻易获得一个静电荷。换言之，保鲜膜随时会产生静电。当你将保鲜膜从卷筒中拉出，或是保鲜膜轻擦过衣袖时，摩擦使得电子转移到保鲜膜的某一区域，进而使该区域产生负电荷。

 

　　而失去电子的表面会产生正电荷。由于异性相吸，不论是装有食物的盘子、衣袖甚至保鲜膜本身的其它部分，保鲜膜都会由于电荷间的相互吸引而与之紧贴在一起。

1 elastic   

n.橡皮圈，松紧带；adj.有弹性的；灵活的

参考例句：

• Rubber is an elastic material.橡胶是一种弹性材料。
• These regulations are elastic.这些规定是有弹性的。

2 elasticity   

n.弹性，伸缩力

参考例句：

• The skin eventually loses its elasticity.皮肤最终会失去弹性。
• Every sort of spring has a definite elasticity.每一种弹簧都有一定的弹性。

3 molecular   

adj.分子的；克分子的

参考例句：

• The research will provide direct insight into molecular mechanisms.这项研究将使人能够直接地了解分子的机理。
• For the pressure to become zero, molecular bombardment must cease.当压强趋近于零时，分子的碰撞就停止了。

4 molecule   

n.分子，克分子

参考例句：

• A molecule of water is made up of two atoms of hygrogen and one atom of oxygen.一个水分子是由P妈̬f婘̬ 妈̬成的。
• This gives us the structural formula of the molecule.这种方式给出了分子的结构式。

5 molecules   

分子( molecule的名词复数 )

参考例句：

• The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
• Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

6 rim   

n.(圆物的)边，轮缘；边界

参考例句：

• The water was even with the rim of the basin.盆里的水与盆边平齐了。
• She looked at him over the rim of her glass.她的目光越过玻璃杯的边沿看着他。

7 friction   

n.摩擦，摩擦力

参考例句：

• When Joan returned to work,the friction between them increased.琼回来工作后，他们之间的摩擦加剧了。
• Friction acts on moving bodies and brings them to a stop.摩擦力作用于运动着的物体，并使其停止。