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This is Scientific American's 60-Second Science. I'm Karen Hopkin. This will just take a minute.

On its opening day, 90,000 tourists traipsed across the London Millennium¹ Bridge. That pitter patter of pedestrian feet caused the structure to visibly rock, earning it the nickname “the wobbly bridge.” Now, in the December 17th issue of the Proceedings² of the Royal Society, civil engineers say they think they know what made the London bridge sway.

It had initially³ been assumed that the movement was caused by a portion of the pedestrians⁴ marching in lock-step. Their synchronized⁵ waddle⁶ could have caused the bridge to oscillate, leading even more of them to tread in tandem⁷. But the engineers say that the same oscillations can be generated by people who are simply plodding⁸ along, just trying to keep their balance—no marching necessary.

Using mathematical modeling, the scientists showed that even walking on level ground people stabilize⁹ themselves by controlling where they place their feet side-to-side. So if they’re walking on a bridge that also wiggles side-to-side, in an effort to keep their balance they may shift their weight even more, making the problem worse. So next time you go to walk across the Thames, remember, the London Millennium Bridge is not falling down. But you still might want to watch your step.

Thanks for the minute for Scientific American's 60-Second Science. I'm Karen Hopkin.

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1 millennium
n.一千年，千禧年；太平盛世
参考例句：
The whole world was counting down to the new millennium.全世界都在倒计时迎接新千年的到来。 We waited as the clock ticked away the last few seconds of the old millennium.我们静候着时钟滴答走过千年的最后几秒钟。

2 proceedings
n.进程，过程，议程；诉讼(程序)；公报
参考例句：
He was released on bail pending committal proceedings. 他交保获释正在候审。 to initiate legal proceedings against sb 对某人提起诉讼

3 initially
adv.最初，开始
参考例句：
The ban was initially opposed by the US.这一禁令首先遭到美国的反对。 Feathers initially developed from insect scales.羽毛最初由昆虫的翅瓣演化而来。

4 pedestrians
n.步行者( pedestrian的名词复数 )
参考例句：
Several pedestrians had come to grief on the icy pavement. 几个行人在结冰的人行道上滑倒了。来自《简明英汉词典》 Pedestrians keep to the sidewalk [footpath]! 行人走便道。来自《现代汉英综合大词典》

5 synchronized
同步的
参考例句：
Do not use the synchronized keyword in Managed Objects. 不要在管理对象上使用synchronized关键字。来自互联网 The timing of the gun was precisely synchronized with the turning of the plane's propeller. 风门的调速与飞机螺旋桨的转动精确同步。来自辞典例句

6 waddle
vi.摇摆地走；n.摇摆的走路(样子)
参考例句：
I am pregnant.I waddle awkwardly and my big stomach pressed against the weight of the world. 我怀孕了，我滑稽可笑地瞒珊而行，大肚子上压着全世界的重量。 We waddle and hop and have lots of fun.我们走起路来摇摇摆摆，还一跳一跳的。我们的生活很有趣。

7 tandem
n.同时发生；配合；adv.一个跟着一个地；纵排地；adj.（两匹马）前后纵列的
参考例句：
Malcolm's contract will run in tandem with his existing one.马尔科姆的合同将与他手头的合同同时生效。 He is working in tandem with officials of the Serious Fraud Office.他正配合欺诈重案办公室的官员工作。

8 plodding
a.proceeding in a slow or dull way
参考例句：
They're still plodding along with their investigation. 他们仍然在不厌其烦地进行调查。 He is plodding on with negotiations. 他正缓慢艰难地进行着谈判。

9 stabilize
vt.（使）稳定，使稳固，使稳定平衡；vi.稳定
参考例句：
They are eager to stabilize currencies.他们急于稳定货币。 His blood pressure tended to stabilize.他的血压趋向稳定。