千禧橋，搖擺橋，下次過橋請小心！

　　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.

　　眾人在橋面行走能使大橋晃動

　　倫敦千禧橋開通的首日，有9萬民游客逛過了這座橋。行人雨點般的步伐致使該橋明顯地晃動，因此千禧橋也得到了“搖擺橋”的綽號。日前，土木工程師們在12月17日的《皇家學會學報》（Proceedings of the Royal Society）撰文說，他們找到了前禧橋晃動的原因。

　　原先的假設是部分行人在橋面上整齊劃一的行走導致了橋的搖晃。他們步調一致的來回走動可能導致了前禧橋的振蕩，這又使得這些行人的步伐更加的一致。但是這些工程師們說，如果人們僅僅在橋面上重步走，只是試圖保持他們的平衡，并沒有齊步走的話，也能導致大橋的來回振蕩。

　　這些科學家們利用數學模型顯示，即使在平地上行走，人們為了保持平衡也是采用兩邊來回行走來達到。所以如果人們在一座來回晃動的橋上行走的話，為了努力保持他們的平衡，他們的重心移動會更大，從而加劇了橋的晃動。所以，下一次如果你要步行走過泰晤士河的話，請放心，千禧橋不會塌掉的。但是你仍然可能會小心翼翼地注意你的步伐