千禧橋，搖擺橋，下次過(guò)橋請(qǐng)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(dòng)

　　倫敦千禧橋開(kāi)通的首日，有9萬(wàn)民游客逛過(guò)了這座橋。行人雨點(diǎn)般的步伐致使該橋明顯地晃動(dòng)，因此千禧橋也得到了“搖擺橋”的綽號(hào)。日前，土木工程師們?cè)?2月17日的《皇家學(xué)會(huì)學(xué)報(bào)》（Proceedings of the Royal Society）撰文說(shuō)，他們找到了前禧橋晃動(dòng)的原因。

　　原先的假設(shè)是部分行人在橋面上整齊劃一的行走導(dǎo)致了橋的搖晃。他們步調(diào)一致的來(lái)回走動(dòng)可能導(dǎo)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(shuō)，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(méi)有齊步走的話，也能導(dǎo)致大橋的來(lái)回振蕩。

　　這些科學(xué)家們利用數(shù)學(xué)模型顯示，即使在平地上行走，人們?yōu)榱吮３制胶庖彩遣捎脙蛇厑?lái)回行走來(lái)達(dá)到。所以如果人們?cè)谝蛔鶃?lái)回晃動(dòng)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(dòng)會(huì)更大，從而加劇了橋的晃動(dòng)。所以，下一次如果你要步行走過(guò)泰晤士河的話，請(qǐng)放心，千禧橋不會(huì)塌掉的。但是你仍然可能會(huì)小心翼翼地注意你的步伐