谢里夫奥尼尔身高:为什么自行车能保持平衡？

Bicycle abuse isn’t something you’d expect from the Dutch. But engineers in the Netherlands who love bikes enough to hurt them are challenging long-held beliefs about how a moving bike keeps its balance even when slapped, shoved or otherwise insulted.

对自行车的“溺爱”可能不光是你从荷兰看到的高普及率，同时，那里热爱自行车的工程师还非得打破砂锅问到底，十分蛋疼地挑战我们固有的观念——关于自行车是怎样保持平衡的，即使在我们的爱车一直被挤被蹭。

The team has found previously unidentified factors that help a bike stay upright and has developed a slew of unusual designs that wouldn’t have been thought to be stable.

这个研究团队发现正是一些我们之前不能察觉的因素使自行车不倒，而且做出了一大批不同寻常的新设计，它们按我们常规思考是不可能保持稳定的。

“We believe there is room for improvement in the handling qualities of bikes,” says Arend Schwab, a professor of engineering mechanics at the Delft University of Technology.

“我们相信要提升自行车的操控性，还是有空间的” Arend Schwab说，这是一位来自德尔福特大学（Delft University）在工程力学领域的专家。 

A conventional bicycle is remarkably stable when moving. Even without a rider, it can coast for long distances and catch itself from falling. As early as 1910, scientists credited this stability to the front wheel behaving like a gyroscope. As a spinning wheel leans, it should naturally swivel in the direction of the lean, guiding the bicycle into a curve that keeps it upright.

一辆传统的自行车在行驶过程中总是非常的稳定。即使没有驾驶者，它也能滑动相当长的距离而不倾倒。早在1910，科学家认为自行车的稳定性靠的是前轮，它有着想陀螺一样的功能。当转轮开始倾斜，它会让龙头顺着倾斜方向转动，牵着车体走出一条曲线保持直立。

In 1970 David E.H. Jones, then a spectroscopist at British chemical company ICI, tested this explanation by trying to build an unridable bike. An extra wheel mounted to its frame spun backwards and canceled out the gyro effect. This bike was less stable -- but still ridable, even with no hands.

在1970年，David E.H. Jones，一名来自英国帝国化工集团（ICI）的一名光谱分析家，为了验证上面的解释，他尝试制作了一辆不能骑的测试自行车。他在后轮的车架上安装了一个附加轮以抵消陀螺效应。这样的自行车只是稳定性变差了——还不至于不能骑，虽然当初没有设计把手。

Jones looked for another stabilizing effect and found one similar to that which keeps the casters of shopping carts lined up. Hold a still bicycle by the seat, lean it to the side and gravity turns the wheel. This “trail effect” is based on the front wheel’s position relative to the angle of the steer axis that connects the wheel to the handlebars. Move the wheel forward a few inches, Jones discovered, and a traditional bike becomes less stable.

Jones 尝试寻找其他的稳定效应来解释，最后得到一个结果，与购物车的脚轮的原理接近。当你扶着一辆车，推它向另一边，重力会使轮子转向。这个“轨道效应”是基于前轮位置与连接轮子和把手的“操控轴”存在有相对的夹角。Jones发现，只要把轮子前推几英尺，一般的自行车就会失去稳定性。

Published in Physics Today, the paper describing these experiments circulated widely and was read by a high school junior in Corvallis, Ore. Jim Papadopoulos, a competitive cyclist, didn’t understand the math at first. But later, in graduate school, its conclusions would bother him.

这篇论文发表在《今日物理》（Physic Today）上，描述了这些实验。它被广泛地阅览，而且也传到美国科瓦利斯一所高中。在这里上学的Ore. Jim Papadopoulos还是一名竞技自行车运动员。当时的他对数学还没有什么认识，知道研究生阶段，这开始困扰他了。

“It took me 30 years to put my finger on the big flaw,” says Papadopoulos, now an engineer at the University of Wisconsin–Stout in Menomonie. “Jones’ paper wasn’t based on the physics of something falling but on the physics of something being held.”

“我花了30年才正视这个”Papadopoulos说，现在的他是位于梅诺莫尼威斯康辛大学斯托特分校的一名工程师。“Jones的论文并不是阐述一种掉落的物理，相反地，他解释了物体维持稳定的原因。”

Papadopoulos teamed up with a researcher from Cornell and a team in the Netherlands that built a bike with no gyroscopic or trail effects. Their riderless contraption, which sports two extra backwards-rotating wheels and a front wheel that touches the ground in front of the steer axis, can still coast stably. Give it a smack, and it curves, swerves and recovers.

Papadopoulos 召集一批康奈尔大学的研究者和一支来自荷兰的队伍，组织成一支新的研究团队。他们致力于制成一种新型的自行车，是不含陀螺和轨迹的。他们的没有驾驶者的新发明，安装有两个反转的轮子，在转向轴之前还有一个触地的轮子，这样在滑行状态也能稳定。如果给它一个侧推，车子将会走出曲线，摆正，然后恢复平衡。

“You don’t need gyroscope or trail to make a bicycle self-stable,” says Andy Ruina, a professor of mechanical engineering at Cornell and coauthor of the paper describing the bike in the April 15 Science.

“为了使自行车自平衡，你并不一定要个陀螺或者轨迹结构”Andy Ruina说，他是来自康奈尔机械工程的教授，并参与了发表在4月15日《科学》上一篇论文的写作。 

Bicycles, the team suggests, are more complicated than previously thought. While gyro and trail effects can contribute to stability, other factors such as the distribution of mass and the bike’s moment of inertia can play a role as well. Computer simulations that take all of these factors into account could lead to improved designs for folding bikes with small wheels or bikes that carry cargo, Ruina says.

这个团队的研究表明自行车要比原来的设想更为复杂。Ruina说，虽然陀螺效应和轨道效应都有助于稳定性的提高，但是还有其他因素诸如质量的分布，车子当时的惯性。计算机模拟能把这些因素进行综合考量。这能改进设计出可折叠或是能拉货的自行车。

To demonstrate the possibilities, the researchers sketched out several new exotic bicycle designs. One is predicted to remain stable even with a negative gyro that tries to turn a falling bicycle in the wrong direction. In another, the steer axis is reversed such that the handlebars are farther forward than the center of the front wheel.

为了证明这一理论的可行性，研究人员勾勒了几种新颖自行车的设计草图。其中一种即使在朝反向作用有负效应陀螺影响下，依然能保持平衡。另外一种，转向轴是翻转的，这样手把就会离前轮中心更远。

“They found a design with rear-wheel steering that can be ridden and is self-stable,” says David Gordon Wilson, a retired MIT professor who designed the modern recumbent bicycle in the early 1970s. “That’s quite amazing.”

“他们发现一种设计加了尾轮，这样可以骑了，也能稳定自身。” MIT的退休教授David Gordon Wilson，曾在上个70年代提出现代倾斜自行车，如是说，“这是在太令人惊奇了。”

In the simulations, these new design principles still work when the weight of a human being is added. But the real test is waiting out on the open road.

在仿真过程中，他们的新设计原则在加上人的重量后依然有效，但是实际结果要上路试一试。

“The next step would be to study a bicycle with a rider in the real world: on actual roads under varying conditions, on a fully instrumented bicycle,” says Joel Fajans, a plasma physicist who also studies bicycles at the University of California, Berkeley.: To find out how we really ride a bike.”

“我们下一步会研究真实中下有驾驶者的情况，实际的路况十分复杂，我们会用一个装满仪器的自行车来测试，这样找到现实中我们是怎样骑车的”Joel Fajans说。他是加州理工伯克利分析的等离子物理学家，现在研究自行车。