英語聽力文摘漂浮的錫紙

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Floating Tin Foil

錫紙為一種涂上或貼以像銀的膜狀金屬紙，多為銀白色，實際上是鋁箔。鋁箔紙(Aluminium foil)，亦作鋁箔，在香港稱之為錫紙，是一種用壓平了的金屬鋁制造的工具，主要用于廚房煮食、盛載食物，或用來制作一些可以簡單清潔的物料。成千上萬噸鋁箔紙在世界各地用作保護和包裝食物、化妝用品和化學制品。大部分的鋁箔紙一面光亮，另外一面灰啞。食品用之鋁箔紙雙面皆可包裹食物，通常建議以光亮面包裹，提升熱傳導效果。最初的錫紙真的是錫造的，錫紙是較鋁箔硬的，也會在食物上帶來一股錫味，故后來鋁價降低后，鋁箔取代了錫紙在日常生活中出現(xiàn)。不過由于金屬鋁會影響腦部發(fā)展，所以現(xiàn)時的鋁箔的表層都會涂有涂層，避免金屬鋁的釋出。

How does tinfoil float? Find out on this Moment of Science.

Here’s an experiment you can do at home with your kids.

Take a sheet of tin foil and shape it into a little canoe. Now fill up the sink(水槽) with water. Now go find a young person. Ask her or him if this much tinfoil will float. Have the young person feel how heavy the tin foil is. After you’ve made your guesses, place the canoe in the water.

Yep, it floats. You say: I guess we can conclude that tin foil that weighs this much is still light enough to float, huh?

If said young person falls for this, say: Then how come when I crumple up(揉皺)the canoe into a ball, the tin foil sinks? Crumple the canoe. Down it goes. The crumpled ball weighs exactly as much as the canoe did. Why doesn’t it float?

The answer is in displacement(位移). An object that displaces(轉移) its own weight in water will float, regardless of how heavy it is. That’s why multi-ton battleships(戰(zhàn)列艦) don’t sink: as long as they push aside their own weight in water, they’ll stay on top.

Now, the canoe you made has an excellent shape for displacing water. It acts like a wedge(楔), pushing water aside as you lower it into the sink and replacing the water with low-density(低密度的) air. The crumpled ball, on the other hand, has just the wrong shape. All of its mass is compressed(壓緊，壓縮) together, so it has a high density throughout and displaces very little water. And down it goes!

注釋：

1.crumple up

(使)坍塌; (揉)皺

The house crumpled up in the gale.

房子在狂風中倒塌了。

It was Jane who crumpled up the document.

是簡把文件弄皺的。

The bus was crumpled up in the crash.

公共汽車在車禍中被撞壞了。

2.displace

及物動詞 vt.

1.(從原來的地方)移開;迫使(人)離開