Floating Tin Foil
锡纸为一种涂上或贴以像银的膜状金属纸，多为银白色，实际上是铝箔。铝箔纸（Aluminium foil），亦作铝箔，在香港称之为锡纸，是一种用压平了的金属铝制造的工具，主要用于厨房煮食、盛载食物，或用来制作一些可以简单清洁的物料。成千上万吨铝箔纸在世界各地用作保护和包装食物、化妆用品和化学制品。大部分的铝箔纸一面光亮，另外一面灰哑。食品用之铝箔纸双面皆可包裹食物，通常建议以光亮面包裹，提升热传导效果。最初的锡纸真的是锡造的，锡纸是较铝箔硬的，也会在食物上带来一股锡味，故后来铝价降低后，铝箔取代了锡纸在日常生活中出现。不过由于金属铝会影响脑部发展，所以现时的铝箔的表层都会涂有涂层，避免金属铝的释出。
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(揉皱)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(转移) its own weight in water will float, regardless of how heavy it is. That’s why multi-ton battleships(战列舰) 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(压紧，压缩) together, so it has a high density throughout and displaces very little water. And down it goes!
注释：
1.crumple up
(使)坍塌; (揉)皱
The house crumpled up in the gale.
房子在狂风中倒塌了。
It was Jane who crumpled up the document.
是简把文件弄皱的。
The bus was crumpled up in the crash.
公共汽车在车祸中被撞坏了。
2.displace
及物动词 vt.
1.(从原来的地方)移开;迫使(人)离开
He displaced a bone in his knee while playing football.
他踢足球时膝盖骨脱臼了。
2.取代,替代
Television has displaced motion pictures as America's most popular form of entertainment.
电视取代了电影的地位,成了美国最为普遍的娱乐方式。
3.撤换;把...免职
4.排(水)
A ship displaces a certain amount of water.
船都有一定的排水量。
3.compress
及物动词 vt.
1.压,压紧,压缩
Wood cuttings and sawdust can be compressed into boards.
木屑和锯末可压制成板。
2.归纳,概括,精简
Can you compress your speech into five minutes?
你能把你的讲话精简为五分钟吗? |