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NARRATOR:Listen to part of a lecture in a materials science class.
MALE PROFESSOR:So what's the first thing that comes to mind when we talk about uses for copper? Tammy?
FEMALE STUDENT:The penny? It's made of copper...
MALE PROFESSOR:Okay, good one... but what's a one-cent coin worth these days?You might get back change, like if you go to the store and give the cashier five dollars for something that costs four dollars ninety-eight cents, you'll get two cents back... but two cents doesn't buy much.The value of the penny in terms of what it'll buy has gotten so low that there's actually a move afoot to eliminate the coin from U.S. currency.
But there's more to it. As Tammy implied, the penny looks like it's solid copper.It's reddish orange, with a bright metallic luster when it's new; but that's just the copper plating.The penny's not solid copper; in actuality, it's almost 98 percent zinc.But, um, given the rising value of both these metals, each penny now costs about 1.7 cents to produce... so it generates what's called negative seigniorage.
Negative seigniorage is when the cost of minting a coin is more than the coin's face value.Even though the penny generates quite a bit of negative seigniorage, there's concern that if it is eliminated, we'll need more nickels— because more merchants might start setting prices in five-cent increments... four dollars ninety-five cents, and so on.So we need a trusty five-cent piece that can be minted economically.But the nickel's negative seigniorage is even worse than the penny's... each nickel costs the U.S. Mint ten cents to produce!
Also, some of us are pretty attached to pennies for whatever reason... nostalgia, and then there's collectors... and people, if they see a penny on the sidewalk, they'll pick it up and think, "It's my lucky day."
Another scenario is that without pennies, merchants, instead of charging four-ninety-eight, might round up the price to an even five dollars.So consumer goods would become slightly more expensive.But, on the other hand, some cash transactions would be more convenient for consumers.And, as I said, the government would save money if pennies were eliminated.
FEMALE STUDENT:But wouldn't the copper industry suffer financially if the U.S. government stopped buying copper to make pennies?
MALE PROFESSOR:[Leadingly, trying to get the student to see her mistake] But how much copper do pennies actually contain?
FEMALE STUDENT:[repeating the question to herself] How much... [realizing her mistake] Oh, got it... right.
MALE PROFESSOR:So, what else comes to mind when you think about copper? [beat—no takers] What else is copper used for?
FEMALE STUDENT:I know that copper can be shaped into all sorts of things: sheets... tubing... My cousin's house has a copper roof.
MALE PROFESSOR:Yes, like gold and silver, copper's extremely malleable, but it's not a precious metal; it's far less expensive than gold or silver.It's also a superb conductor of electricity, so you can stretch it into wires, which go into appliances and even car motors.
Copper also has superior alloying properties—[clarifying] it's, y'know, when it's combined with other metals.For instance, how many of you play a brass instrument, like a trumpet or trombone?Well, brass is an alloy of copper and zinc. If your trombone was made of pure copper or pure zinc, it wouldn't sound nearly as beautiful as a brass trombone.
Another alloy, a combination of copper and nickel, resists corrosion... it doesn't rust, even with prolonged exposure to water.
FEMALE STUDENT:But what about the Statue of Liberty, in New York Harbor? It's made of pure copper, but it turned green. Isn't that a sign of corrosion?
MALE PROFESSOR:Indirectly. If copper's exposed to damp air, its color changes from reddish orange to reddish brown.But, in time, a green film called a "patina" forms, and the patina actually serves to halt any further corrosion.It's one reason that ship hulls are made of copper-nickel alloys.These alloys are also hard for barnacles to stick to. If these little shellfish adhere to the hull of a ship, it produces drag, slowing the vessel down.
Copper's also a key material used in solar-heating units and in water-desalination plants, which are playing increasingly important roles in society.
Bottom line? If you're a copper miner, you won't lose any sleep should the penny get—if you'll excuse the expression—pinched out of existence.
旁白：请听材料科学课上的部分内容。
教授：提到铜的用途时，你们的脑海中会最先出现什么？Tammy，你来说？
学生：便士，它是用铜做的。
教授：不错的例子，但是如今一个一分钱的硬币值多少呢？你可能会拿回找零，比如，如果你去商店，然后买了某个4.98美元的东西，你给了收银员5美元，会得到2分钱的找零，但是2两分钱买不了什么。便士在购买力方面的价值变得非常低，以至于事实上现在正在进行一个从美国货币中淘汰这种面额的硬币的行动。
但是并不仅因为这个原因。正如Tammy所说，便士看上去像纯铜的。新便士是红褐色的，带有一层亮金属光泽，但那只是镀铜的。便士不是纯铜的，事实上，它的材质几乎98%都是锌。但是考虑到这两种金属的价值都在上涨，现在每个便士的制造成本约1.7分钱，所以它产生了负铸币利差。
负铸币利差就是铸造一枚硬币的成本高于这个硬币的面值。虽然便士产生了负铸币利差，但是有人担心如果淘汰了它，我们就会需要更多五分钱，因为更多的商家可能会开始给价格定五分钱的增额，比如4.95美元等等。所以我们需要能划算地铸造可靠的五分硬币。但是五分硬币的负铸币利差比便士还更严重，美国铸币厂每制造一枚五分硬币要花10分钱。
还有，我们中一些人出于某种原因，比如怀旧和收藏，对便士青睐有加。而且，如果人们在路上看到了一分钱，他们会把它捡起来然后想着：“今天是我的幸运日！”
另一个情况是，没有了一分钱硬币，商人们不会标价4.98美元，而是可能甚至把价格四舍五入提高到五美元。所以消费品会变得稍贵一些。但是从另一方面来看，对消费者来说一些现金交易会更方便。而且就像我说过的，如果淘汰了便士，政府能省下不少钱。
学生：但是如果美国政府不再购买铜来制作便士了，铜业不就有经济损失了吗？
教授：但是便士中究竟含了多少铜呢？
学生：多少......哦，我知道了，没错。
教授：那么，提到铜你还能想到别的什么？铜还有什么用处？
学生：我知道铜能做成各种东西：铜片、管子，我表哥的房子有一个铜做的屋顶。
教授：是的，和黄金白银一样，铜的可塑性极强，但它不是贵金属，比黄金白银便宜多了。它也是一种极好的导电体，所以你可以把它抻拉成电线，装进电器甚至汽车引擎里。
铜的合金性质也很优越，也就是它能和其他金属结合在一起。举个例子来说，你们中玩铜管乐器的人多不多，比如喇叭或者长号？铜管乐器是铜和锌的合金，如果你的长号是用纯铜或者纯锌制作的，它演奏起来就不如铜锌合金的听起来美妙。
另一种合金是铜镍合金，抗腐蚀性很强。即使长时间浸在水中，它也不会生锈。
学生：但是纽约港的自由女神像呢？它是由纯铜制作的，但是却变成了绿色，那不是腐蚀的迹象吗？
教授：间接地。如果铜暴露在湿润的空气中，它的颜色会从红褐色变成红棕色。但是，随时间推移会形成一层叫做铜绿的绿色薄膜，铜绿实际上起着阻止进一步腐蚀的作用。船体用通镍合金制作的原因之一就是这个。甲壳动物还很难粘附在这些合金上。如果这些小型甲壳动物粘在了船体上，就会产生拖力，减慢船速。
铜还是太阳能加热装置和水体淡化工厂使用的一种关键材料，它在社会中的作用将越来越重要。
概括来说：如果你是铜矿工人，万一便士取缔了，你也不会担心得睡不着觉，请原谅我的用语。