一夜之間，彷彿全世界的人都在立掃把，你的朋友圈被五花八門的立掃把圖片刷屏了嗎？
昨天，一則據傳來自NASA（美國國家航空航天局）的消息稱，“因為今天地球完美的重力角度，是唯一一天可以讓掃把獨自站立的日子。”
微博截圖
於是各路網友紛紛加入“立掃把”挑戰（broomstick challenge）……
據外媒報道，該挑戰最初源於一條推特，隨後風靡整個社交網絡。
The challenge originated from a viral tweet, which claimed that NASA said Monday was the only day a broomstick could stand on its own because of the earth's gravitational pull. The tweet was accompanied by a video of a woman propping a broom up. As the woman watches the broom stand up on its own, she yells, "No strings, nothing."
該挑戰源於一條熱門推特，推文宣稱NASA說因為引力原因，（當地時間）週一是唯一可以讓掃把獨自立起來的日子。這條推特還配了段一名女子立掃把的視頻。這名女子看到掃把獨自立著，高呼“沒有繩，啥都沒有！”
大家紛紛把自己立掃把的圖片和視頻上傳到網絡，驚呼“我的天吶！”
而這個“立掃把挑戰”也火速傳至國內，引發了開頭提到的掃把圖片刷屏大賽。 那麼究竟為什麼掃帚能立住呢？
▌中科大副研究員：主要是手法問題，和日子沒關係
中科大副研究員袁嵐峰經過計算表示，太陽對掃帚的引力，大約為地球引力的五十億分之一。地球繞太陽軌道近似一個圓，太陽微小的引力變化又很小。
Yuan Lanfeng, an associate professor at the University of Science and Technology of China, said that the sun’s gravity acting on the broom is about one five billionth that of the Earth. Moreover, that gravity changes little with time as the Earth’s orbit around the sun is almost round.
而立掃帚是一個宏觀的行為，影響它的力不可能這麼精細，所以這一定是個謠言。如果你能立起來，那是因為你掌握了手法，那麼你在任何一天都能立起來。如果立不起來，不妨多學習學習手法，等日子是沒有用的。
It is expecting too much to believe such a micro force will affect whether the broom stands upright. If you can make a broom stand up one day, you can do it on any other day — There is nothing special with the date.
▌科普大V：只要你想立，天天都能立起來
物理學博士後、科普大V@賊叉解釋稱，物體上每個點所受的重力可以等效為一個點受重力，此即為物體的重心。重心投影在地面上時，如果在支撐點範圍內，那就能站住；超出了支撐點範圍，那就摔倒了，所以接觸面越大越容易立住。掃帚頭朝下站住並不是什麼很稀罕的事情。
Zei Cha, a post-doctorate scholar in physics, explained that each object has a point called its center of gravity. As long as its shadow cast on the ground is within the range of support points, the object can stand. Thus the bigger the contact surface, the easier it is to stand. So it is not so hard to make a broom stand on its head.
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