千禧桥，摇摆桥，下次过桥请小心！

　　On its opening day, 90,000 tourists traipsed across the London Millennium 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 Proceedings of the Royal Society, civil engineers say they think they know what made the London bridge sway.

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

　　Using mathematical modeling, the scientists showed that even walking on level ground people stabilize 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.

　　众人在桥面行走能使大桥晃动

　　伦敦千禧桥开通的首日，有9万民游客逛过了这座桥。行人雨点般的步伐致使该桥明显地晃动，因此千禧桥也得到了“摇摆桥”的绰号。日前，土木工程师们在12月17日的《皇家学会学报》（Proceedings of the Royal Society）撰文说，他们找到了前禧桥晃动的原因。

　　原先的假设是部分行人在桥面上整齐划一的行走导致了桥的摇晃。他们步调一致的来回走动可能导致了前禧桥的振荡，这又使得这些行人的步伐更加的一致。但是这些工程师们说，如果人们仅仅在桥面上重步走，只是试图保持他们的平衡，并没有齐步走的话，也能导致大桥的来回振荡。

　　这些科学家们利用数学模型显示，即使在平地上行走，人们为了保持平衡也是采用两边来回行走来达到。所以如果人们在一座来回晃动的桥上行走的话，为了努力保持他们的平衡，他们的重心移动会更大，从而加剧了桥的晃动。所以，下一次如果你要步行走过泰晤士河的话，请放心，千禧桥不会塌掉的。但是你仍然可能会小心翼翼地注意你的步伐