托福閱讀資料之How Do You Make A Diet-Coke Float?

　　Take a can of “classic” Coca-Cola and a can of Diet Coke, and without opening either one submerge them in water. A deep sink or a bucket will do the trick. You’ll find the can of Diet Coke rises to the top, while the Classic Coke stays sunk. Can you guess why?

　　Why?

　　The answer lies in the chemical contents of the Diet Coke —in fact, in the very distinction that makes it “Diet”.

　　Although their ingredients are otherwise similar, Diet Coke is not made with real sugar: instead, the makers of Coca-Cola products have replaced the sugar with a synthetic chemical called Aspartame.

　　Aspartame, which is commonly known as Nutrasweet, is a kind of substitute sugar —intended to mimic the distinctive taste of sugar without carrying the associated calories.

　　High Molecular Density

　　Real sugar has a high molecular density. In other words you can think of sugar molecules as being thickly packed together.

　　This also means sugar molecules themselves will be relatively heavy, even when dissolved in solution. In the case of the sinking Coke, the real sugar content is acting as an anchor for the can.

　　Coca-Cola Taste

　　There’s also the fact that Nutrasweet is much sweeter than sugar, and so less is needed per can to achieve that recognizable Coca-Cola taste. Thus the bobbing Diet Coke not only has a lower average density, it also has a lower mass —there’s less “stuff” dissolved in the mixture. If you were an advertising executive, you might want to market diet sodas as “Light” —it wouldn’t be far from the truth.

　　你可以在家做這樣的實(shí)驗(yàn)。

　　把沒(méi)打開(kāi)過(guò)的兩聽(tīng)可樂(lè)(含糖，無(wú)糖)放在深槽或者高桶中，里面的水淹沒(méi)兩聽(tīng)可樂(lè)，你會(huì)發(fā)現(xiàn)無(wú)糖可樂(lè)浮在水面;而含糖可樂(lè)卻沉下去了。你能猜到原因嗎?

　　奧秘就在于無(wú)糖可樂(lè)的成分，這也是“無(wú)糖”的原因。雖然，無(wú)糖可樂(lè)和普通可樂(lè)的成分很相似，無(wú)糖可樂(lè)中添加的并非真正的糖，而是一種做“阿斯巴甜”的合成化學(xué)物。

　　“阿斯巴甜”是一種常見(jiàn)的代糖甜味劑，不含糖的熱量卻有糖的甜味。

　　高分子密度

　　真正的糖分子密度高，也就是說(shuō)糖分子緊密地排列在一起。

　　即使溶解在溶液中，相同體積的糖更重。實(shí)驗(yàn)中沉下去的普通可樂(lè)，正是因?yàn)樘浅煞窒皴^般讓罐子下沉。

　　可樂(lè)的味道

　　代糖比糖甜，所以更少的代糖能達(dá)到普通可樂(lè)的甜味。這樣水中搖擺的無(wú)糖可樂(lè)不僅平均密度更低，質(zhì)量也比普通可樂(lè)輕——因?yàn)楦俚拇侨芙庠诳蓸?lè)中。如果你是廣告商，你可以這樣宣傳——無(wú)糖碳酸飲料的優(yōu)點(diǎn)：輕。這可沒(méi)有說(shuō)大話。