為什么萵苣姑娘的頭發(fā)能當(dāng)繩梯

景一

☆Hair is much， much stronger than you might expect. 頭發(fā)比你想象的要結(jié)實得多。

Rapunzels incredibly long hair makes a great rope ladder in the fairy tale. But could that work in reality？

在童話中，萵苣姑娘（又名長發(fā)公主）長得令人難以置信的頭發(fā)可以作為很棒的繩梯。但是，這在現(xiàn)實中能起作用嗎？

In the classic fairy tale， the princess Rapunzel is trapped high in a tower. A dashing prince comes to rescue her. “Rapunzel， Rapunzel， let down your hair，” he calls. She unfurls her lengthy locks， draping them out the tower window. The prince then climbs up that magic hair to rescue his lady love. The story is obviously fiction. But there may be a little truth behind a human hair-based escape. Science， it turns out， has found that hair is some super strong stuff. A prince （or princess） would actually have few problems climbing a rope made of human hair. The challenge would be growing such a lengthy mane1 in the first place.

在經(jīng)典的童話故事中，萵苣姑娘被困在高塔中。一位英俊的王子來救她。“萵苣，萵苣，把你的頭發(fā)放下，”他喊道。她解開長長的發(fā)辮，從塔樓的窗戶上垂下來。然后王子爬上那神奇的頭發(fā)來拯救他的愛人。這個故事顯然是虛構(gòu)的。但在一個以頭發(fā)為基礎(chǔ)的逃亡故事的背后，可能有點道理?？茖W(xué)證明，頭發(fā)是一種非常結(jié)實的東西。一個王子（或公主）攀登一根由人發(fā)制成的繩子幾乎沒有問題。最首要的困難是要長這么長的頭發(fā)。

Hair is strong. Really strong. A single human hair can take a force of 200 megapascals2. This is its tensile3 strength—how much load it can take before breaking. Pressure is measured in pascals4. A pascal is the amount of mass something can take per square meter of material. One megapascal is 1，000，000 pascals. In the case of a human hair， 200 megapascals is 20，000，000 kilograms of force per square meter of human hair.

頭發(fā)很結(jié)實。真的很結(jié)實。一根頭發(fā)能承受200兆帕的壓力。這是它的拉伸強度——即斷裂前它能承受多少負(fù)荷。壓力的測量單位是帕斯卡。帕斯卡是每平方米材料所能承受的質(zhì)量。一兆帕等于一百萬帕斯卡。如果是人的頭發(fā)，200兆帕等于每平方米的頭發(fā)承受2000萬公斤的力。

Those are some big numbers. “They mean that a single strand of hair is about half as strong as a piece of steel the same size，” notes Ray Goldstein. He studies biological physics at the University of Cambridge in England. Among the things hes studied is the physics of ponytails.

這是很大的數(shù)字?！斑@意味著一股頭發(fā)的強度有一塊同樣大小鋼鐵的一半，”雷·戈爾茨坦解釋說。他在英國劍橋大學(xué)學(xué)習(xí)生物物理學(xué)，研究的內(nèi)容是馬尾辮的物理學(xué)。

Wen Yang is a materials scientist at the University of California in San Diego. Shes performed studies on the strength of human hair. She has compared hairs strength to a finger lifting a loaded shopping bag. Not just any bag of food. If your finger were as strong as a bundle of human hair the same size， that one bag could hold 11，340，000 kilograms！

楊文（音譯）是圣迭戈加州大學(xué)的材料科學(xué)家，她對人類頭發(fā)的強度進(jìn)行了研究。她將頭發(fā)的力量與提著一個裝滿的購物袋的手指進(jìn)行對比。不只是一袋食物。如果你的手指和一束同樣粗細(xì)的頭發(fā)一樣結(jié)實，那么你的手指可以提起裝著1134萬公斤物品的袋子！

Hairs secret comes from its structure， Yang explains. “You might use an example of the Russian matryoshka doll5，” she says. “Inside the biggest doll （the hair）， there are millions or more of the smaller dolls.” Those smaller dolls are tiny protein6 chains. Theyre contained within an area called the cortex7. The chains are layered together and covered with an outer coating called the cuticle8. “The cuticle looks like a fish scale，” Yang says. It holds the protein bundles of the cortex together.

楊解釋說，頭發(fā)的秘密來自于結(jié)構(gòu)。“你可以用俄羅斯套娃舉例，”她說?！霸谧畲蟮耐尥蓿^發(fā)）里面，有上百萬個或更多的小娃娃?！蹦切┬⊥尥奘俏⑿〉牡鞍踪|(zhì)鏈。它們被包裹在叫做毛皮質(zhì)的區(qū)域內(nèi)。這些鏈條是分層的，外面覆蓋的一層叫做毛表皮。“毛表皮看起來像魚鱗，”楊說，它將毛皮質(zhì)的蛋白質(zhì)鏈?zhǔn)谝黄稹?/p>

Rapunzels hair is not only strong but also very long. That length might make her mane overall a little weaker， Rhett Allain notes. Hes a physicist at Southeastern Louisiana University in Hammond. Hairs protein chains， he says， are “l(fā)ittle atoms9 connected by springs”. If you pull too strongly， the spring breaks. No chain is perfect. In fact， a longer chain is more likely to have a weak point that snaps10 under the load. Rapunzel gets around this problem by throwing down a big braid or ponytail of hair， instead of a single strand. The individual protein chains might be weak， but theyre strong when bound together.

萵苣姑娘的頭發(fā)不僅結(jié)實，而且很長。瑞德·艾倫指出，這樣的長度可能會使她的頭發(fā)整體上變?nèi)跻恍?。瑞德·艾倫是哈蒙德的東南路易斯安那大學(xué)的物理學(xué)家。他說，頭發(fā)的蛋白質(zhì)鏈?zhǔn)恰坝蓮椈蛇B接的小原子”。如果拉力太大，彈簧就會斷裂，沒有鏈條是完美的。事實上，較長的鏈條更有可能有薄弱點在負(fù)載下發(fā)生斷裂。萵苣姑娘拋下一根大辮子或馬尾辮，而不是一股頭發(fā)，解決了這個問題。個別的蛋白質(zhì)鏈可能是脆弱的，但當(dāng)它們結(jié)合在一起時很結(jié)實。

So strong， in fact， that Yang and Goldstein both estimate that some 500 to 1，000 hairs could support a full-grown human weighing about 80 kg. Thats not much hair. “A typical human head has about 50，000 to 100，000 hairs，” Goldstein notes.

事實上相當(dāng)結(jié)實，楊和戈爾茨坦都認(rèn)為大約500到1000根頭發(fā)可以承受一個體重約80公斤的成年人。那不算太多頭發(fā)?！耙粋€普通人類頭部有大約5萬到10萬根頭發(fā)，”戈爾茨坦解釋說。

The prince couldnt just yank on the hair， though. “Keep in mind the hair is attached to the head via biological structures，” Goldstein says. Those structures are called follicles11. And these arent as strong as hair. A single hair can easily be yanked12 out. So while the hair could take the weight， the scalp13 might suffer. The solution is to loop the long hair around a pole or hook， creating a pulley14 that keeps Rapunzels hair attached to her head.

但王子不能只是猛拉頭發(fā)?！坝涀?，頭發(fā)是通過生物結(jié)構(gòu)附著在頭上的，”戈爾茨坦說。這些結(jié)構(gòu)被稱為毛囊，而且它們不像頭發(fā)那么結(jié)實。一根頭發(fā)很容易被拔出來。所以，雖然頭發(fā)可以承受重量，但頭皮可能會受損。解決方法是將長發(fā)繞在一根桿子或鉤子上，做成一個滑輪，使長發(fā)好好地留在萵苣姑娘的頭上。

Hair is both strong and flexible， and clearly would make a climbable rope. Why dont we use it that way？ In the past， Yang notes， people did use human hair for some things， such as sewing skin closed in surgery. But as a natural material， hair easily breaks down in the environment， Yang says. Not only that， the proteins in hair can be affected by temperature and the amount of water in the air. Artificial15 materials are more consistent.

頭發(fā)既結(jié)實又柔韌，很明顯會成為一條可攀爬的繩子。為什么我們不那樣使用它呢？楊指出，在過去，人們確實用頭發(fā)做一些事情，比如用在手術(shù)縫合皮膚中。但楊說，頭發(fā)作為一種天然材料，在環(huán)境中很容易分解。不僅如此，頭發(fā)中的蛋白質(zhì)還可能受到溫度和空氣中水分的影響。人工材料更加穩(wěn)定。

Hair also is pretty slick， Goldstein notes. Even when twisted into rope， he says， hair might be too slippery to hold together well. Regular rope makes for an easier climb.

戈爾茨坦指出，頭發(fā)也相當(dāng)光滑。他說，即使把頭發(fā)擰成繩子，頭發(fā)也可能因為太滑而無法很好地固定在一起。普通的繩子爬起來更容易。

And of course， theres the cultural aspect. “I think people would be squeamish16 about using human parts for anything like that，” Goldstein says.

當(dāng)然，還有文化方面的原因?！拔艺J(rèn)為人們對用人體的部分做那樣的事情感到局促不安，”戈爾茨坦說。

But hairs final weakness is that it grows slowly. The average human hair grows about 15 cm per year. At that rate， if Rapunzel were trapped in a tower 10 meters tall （about as tall as a four-story building）， it would take 66.6 years for her hair to grow long enough to reach the base. Thats a long time to wait for a rescue.

但頭發(fā)最后的弱點是生長緩慢。人類平均每年頭發(fā)生長約15厘米。以這樣的速度，如果萵苣姑娘被困在一座10米高的塔中（大約有四層樓高），她的頭發(fā)需要66.6年才能長到足以到達(dá)地面的長度，那樣等待救援的時間太長了。

Notes

1. mane? ?n. 鬃毛

2. megapascal? n. 兆帕（壓強單位）

3. tensile adj. 拉力的

4. pascal? ?n. 帕斯卡（壓強的單位）

5. Russian matryoshka doll 俄羅斯套娃

6. protein? ?n. 蛋白質(zhì)

7. cortex? ?n. 皮質(zhì)

8. cuticle? ?n. 角質(zhì)層;表皮

9. atom? n. 原子

10. snap vt. 突然折斷，拉斷

11. follicle n. （皮膚上的）毛囊

12. yank? vt. 猛拉

13. scalp? n. 頭皮

14. pulley? n. 滑輪

15. artificial? ?adj. 人造的

16. squeamish? adj. 神經(jīng)質(zhì)的