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☆Hair is much， much stronger than you might expect. 头发比你想象的要结实得多。
Rapunzel’s incredibly long hair makes a great rope ladder in the fairy tale. But could that work in reality？
在童话中，莴苣姑娘（又名长发公主）长得令人难以置信的头发可以作为很棒的绳梯。但是，这在现实中能起作用吗？
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.
在經典的童话故事中，莴苣姑娘被困在高塔中。一位英俊的王子来救她。“莴苣，莴苣，把你的头发放下，”他喊道。她解开长长的发辫，从塔楼的窗户上垂下来。然后王子爬上那神奇的头发来拯救他的爱人。这个故事显然是虚构的。但在一个以头发为基础的逃亡故事的背后，可能有点道理。科学证明，头发是一种非常结实的东西。一个王子（或公主）攀登一根由人发制成的绳子几乎没有问题。最首要的困难是要长这么长的头发。
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.
头发很结实。真的很结实。一根头发能承受200兆帕的压力。这是它的拉伸强度——即断裂前它能承受多少负荷。压力的测量单位是帕斯卡。帕斯卡是每平方米材料所能承受的质量。一兆帕等于一百万帕斯卡。如果是人的头发，200兆帕等于每平方米的头发承受2000万公斤的力。
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 he’s studied is the physics of ponytails.
这是很大的数字。“这意味着一股头发的强度有一块同样大小钢铁的一半，”雷·戈尔茨坦解释说。他在英国剑桥大学学习生物物理学，研究的内容是马尾辫的物理学。
Wen Yang is a materials scientist at the University of California in San Diego. She’s performed studies on the strength of human hair. She has compared hair’s 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！
杨文（音译）是圣迭戈加州大学的材料科学家，她对人类头发的强度进行了研究。她将头发的力量与提着一个装满的购物袋的手指进行对比。不只是一袋食物。如果你的手指和一束同样粗细的头发一样结实，那么你的手指可以提起装着1134万公斤物品的袋子！ Hair’s 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. They’re 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.
杨解释说，头发的秘密来自于结构。“你可以用俄罗斯套娃举例，”她说。“在最大的娃娃（头发）里面，有上百万个或更多的小娃娃。”那些小娃娃是微小的蛋白质链。它们被包裹在叫做毛皮质的区域内。这些链条是分层的，外面覆盖的一层叫做毛表皮。“毛表皮看起来像鱼鳞，”杨说，它将毛皮质的蛋白质链束在一起。
Rapunzel’s hair is not only strong but also very long. That length might make her mane overall a little weaker， Rhett Allain notes. He’s a physicist at Southeastern Louisiana University in Hammond. Hair’s protein chains， he says， are “little 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 they’re strong when bound together.
莴苣姑娘的头发不仅结实，而且很长。瑞德·艾伦指出，这样的长度可能会使她的头发整体上变弱一些。瑞德·艾伦是哈蒙德的东南路易斯安那大学的物理学家。他说，头发的蛋白质链是“由弹簧连接的小原子”。如果拉力太大，弹簧就会断裂，没有链条是完美的。事实上，较长的链条更有可能有薄弱点在负载下发生断裂。莴苣姑娘抛下一根大辫子或马尾辫，而不是一股头发，解决了这个问题。个别的蛋白质链可能是脆弱的，但当它们结合在一起时很结实。
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. That’s not much hair. “A typical human head has about 50，000 to 100，000 hairs，” Goldstein notes.
事实上相当结实，杨和戈尔茨坦都认为大约500到1000根头发可以承受一个体重约80公斤的成年人。那不算太多头发。“一个普通人类头部有大约5万到10万根头发，”戈尔茨坦解释说。
The prince couldn’t 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 aren’t 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 Rapunzel’s hair attached to her head.
但王子不能只是猛拉头发。“记住，头发是通过生物结构附着在头上的，”戈尔茨坦说。这些结构被称为毛囊，而且它们不像头发那么结实。一根头发很容易被拔出来。所以，虽然头发可以承受重量，但头皮可能会受损。解决方法是将长发绕在一根杆子或钩子上，做成一个滑轮，使长发好好地留在莴苣姑娘的頭上。
Hair is both strong and flexible， and clearly would make a climbable rope. Why don’t 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. 头发既结实又柔韧，很明显会成为一条可攀爬的绳子。为什么我们不那样使用它呢？杨指出，在过去，人们确实用头发做一些事情，比如用在手术缝合皮肤中。但杨说，头发作为一种天然材料，在环境中很容易分解。不仅如此，头发中的蛋白质还可能受到温度和空气中水分的影响。人工材料更加稳定。
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.
戈尔茨坦指出，头发也相当光滑。他说，即使把头发拧成绳子，头发也可能因为太滑而无法很好地固定在一起。普通的绳子爬起来更容易。
And of course， there’s the cultural aspect. “I think people would be squeamish16 about using human parts for anything like that，” Goldstein says.
当然，还有文化方面的原因。“我认为人们对用人体的部分做那样的事情感到局促不安，”戈尔茨坦说。
But hair’s 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. That’s a long time to wait for a rescue.
但头发最后的弱点是生长缓慢。人类平均每年头发生长约15厘米。以这样的速度，如果莴苣姑娘被困在一座10米高的塔中（大约有四层楼高），她的头发需要66.6年才能长到足以到达地面的长度，那样等待救援的时间太长了。
Notes
1. mane
Rapunzel’s incredibly long hair makes a great rope ladder in the fairy tale. But could that work in reality？
在童话中，莴苣姑娘（又名长发公主）长得令人难以置信的头发可以作为很棒的绳梯。但是，这在现实中能起作用吗？
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.
在經典的童话故事中，莴苣姑娘被困在高塔中。一位英俊的王子来救她。“莴苣，莴苣，把你的头发放下，”他喊道。她解开长长的发辫，从塔楼的窗户上垂下来。然后王子爬上那神奇的头发来拯救他的爱人。这个故事显然是虚构的。但在一个以头发为基础的逃亡故事的背后，可能有点道理。科学证明，头发是一种非常结实的东西。一个王子（或公主）攀登一根由人发制成的绳子几乎没有问题。最首要的困难是要长这么长的头发。
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.
头发很结实。真的很结实。一根头发能承受200兆帕的压力。这是它的拉伸强度——即断裂前它能承受多少负荷。压力的测量单位是帕斯卡。帕斯卡是每平方米材料所能承受的质量。一兆帕等于一百万帕斯卡。如果是人的头发，200兆帕等于每平方米的头发承受2000万公斤的力。
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 he’s studied is the physics of ponytails.
这是很大的数字。“这意味着一股头发的强度有一块同样大小钢铁的一半，”雷·戈尔茨坦解释说。他在英国剑桥大学学习生物物理学，研究的内容是马尾辫的物理学。
Wen Yang is a materials scientist at the University of California in San Diego. She’s performed studies on the strength of human hair. She has compared hair’s 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！
杨文（音译）是圣迭戈加州大学的材料科学家，她对人类头发的强度进行了研究。她将头发的力量与提着一个装满的购物袋的手指进行对比。不只是一袋食物。如果你的手指和一束同样粗细的头发一样结实，那么你的手指可以提起装着1134万公斤物品的袋子！ Hair’s 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. They’re 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.
杨解释说，头发的秘密来自于结构。“你可以用俄罗斯套娃举例，”她说。“在最大的娃娃（头发）里面，有上百万个或更多的小娃娃。”那些小娃娃是微小的蛋白质链。它们被包裹在叫做毛皮质的区域内。这些链条是分层的，外面覆盖的一层叫做毛表皮。“毛表皮看起来像鱼鳞，”杨说，它将毛皮质的蛋白质链束在一起。
Rapunzel’s hair is not only strong but also very long. That length might make her mane overall a little weaker， Rhett Allain notes. He’s a physicist at Southeastern Louisiana University in Hammond. Hair’s protein chains， he says， are “little 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 they’re strong when bound together.
莴苣姑娘的头发不仅结实，而且很长。瑞德·艾伦指出，这样的长度可能会使她的头发整体上变弱一些。瑞德·艾伦是哈蒙德的东南路易斯安那大学的物理学家。他说，头发的蛋白质链是“由弹簧连接的小原子”。如果拉力太大，弹簧就会断裂，没有链条是完美的。事实上，较长的链条更有可能有薄弱点在负载下发生断裂。莴苣姑娘抛下一根大辫子或马尾辫，而不是一股头发，解决了这个问题。个别的蛋白质链可能是脆弱的，但当它们结合在一起时很结实。
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. That’s not much hair. “A typical human head has about 50，000 to 100，000 hairs，” Goldstein notes.
事实上相当结实，杨和戈尔茨坦都认为大约500到1000根头发可以承受一个体重约80公斤的成年人。那不算太多头发。“一个普通人类头部有大约5万到10万根头发，”戈尔茨坦解释说。
The prince couldn’t 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 aren’t 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 Rapunzel’s hair attached to her head.
但王子不能只是猛拉头发。“记住，头发是通过生物结构附着在头上的，”戈尔茨坦说。这些结构被称为毛囊，而且它们不像头发那么结实。一根头发很容易被拔出来。所以，虽然头发可以承受重量，但头皮可能会受损。解决方法是将长发绕在一根杆子或钩子上，做成一个滑轮，使长发好好地留在莴苣姑娘的頭上。
Hair is both strong and flexible， and clearly would make a climbable rope. Why don’t 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. 头发既结实又柔韧，很明显会成为一条可攀爬的绳子。为什么我们不那样使用它呢？杨指出，在过去，人们确实用头发做一些事情，比如用在手术缝合皮肤中。但杨说，头发作为一种天然材料，在环境中很容易分解。不仅如此，头发中的蛋白质还可能受到温度和空气中水分的影响。人工材料更加稳定。
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.
戈尔茨坦指出，头发也相当光滑。他说，即使把头发拧成绳子，头发也可能因为太滑而无法很好地固定在一起。普通的绳子爬起来更容易。
And of course， there’s the cultural aspect. “I think people would be squeamish16 about using human parts for anything like that，” Goldstein says.
当然，还有文化方面的原因。“我认为人们对用人体的部分做那样的事情感到局促不安，”戈尔茨坦说。
But hair’s 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. That’s a long time to wait for a rescue.
但头发最后的弱点是生长缓慢。人类平均每年头发生长约15厘米。以这样的速度，如果莴苣姑娘被困在一座10米高的塔中（大约有四层楼高），她的头发需要66.6年才能长到足以到达地面的长度，那样等待救援的时间太长了。
Notes
1. mane