“立扫把挑战”刷屏，NASA出来辟谣：It's just physics.

一夜之间，仿佛全世界的人都在立扫把，你的朋友圈被五花八门的立扫把图片刷屏了吗？

昨天，一则据传来自NASA（美国国家航空航天局）的消息称，“因为今天地球完美的重力角度，是唯一一天可以让扫把独自站立的日子。”

微博截图

于是各路网友纷纷加入“立扫把”挑战（broomstick challenge）……

这则消息到底是怎么来的呢，双语君（微信ID：Chinadaily_Mobile）搜索了一下。

据外媒报道，该挑战最初源于一条推特，随后风靡整个社交网络。

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.'

该挑战源于一条热门推特，推文宣称NASA说因为引力原因，（当地时间）周一是唯一可以让扫把独自立起来的日子。这条推特还配了段一名女子立扫把的视频。这名女子看到扫把独自立着，高呼“没有绳，啥都没有！”

大家纷纷把自己立扫把的图片和视频上传到网络，惊呼“我的天呐！”

而这个“立扫把挑战”也火速传至国内，引发了开头提到的扫把图片刷屏大赛。

那么究竟为什么扫帚能立住呢？双语君（微信ID：Chinadaily_Mobile）就此请教了几位物理学家。

▌中科大副研究员：主要是手法问题，和日子没关系

中科大副研究员袁岚峰经过计算表示，太阳对扫帚的引力，大约为地球引力的五十亿分之一。地球绕太阳轨道近似一个圆，太阳微小的引力变化又很小。

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.

而立扫帚是一个宏观的行为，影响它的力不可能这么精细，所以这一定是个谣言。如果你能立起来，那是因为你掌握了手法，那么你在任何一天都能立起来。如果立不起来，不妨多学习学习手法，等日子是没有用的。

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，天天都能立起来

物理学博士后、科普大V@贼叉解释称，物体上每个点所受的重力可以等效为一个点受重力，此即为物体的重心。重心投影在地面上时，如果在支撑点范围内，那就能站住；超出了支撑点范围，那就摔倒了，所以接触面越大越容易立住。扫帚头朝下站住并不是什么很稀罕的事情。

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.

图源见水印

至于扫帚柄朝下也能立住的人，可能是在家憋太久，达到了熟能生巧的境界。

Yet it requires skills and perhaps repeated practice to make a broom stand on the sharp end.

这位博士后还秀了句英语：

“If you are bored enough, you can make a broom stand every day.”

▌中科院物理所博士：找到平衡点，万物皆可立

中科院物理所博士樊秦凯指出，立住的关键在于找到平衡点，大多数时候物体立不住，主要是因为很难找到平衡点，而且平衡点经常很不稳定，稍微一干扰就倒了。

Fan Qinkai, a doctorate student at the Institute of Physics, Chinese Academy of Sciences, said that the key to making a broom stand upright lies in finding the balance point. 

扫帚能立住，因为它的毛比较硬且有弹性，两侧的毛互相朝外一弯曲，就有弹力，增强了稳定性。

The hairy end of a broom is quite hard and elastic, so when the hairs split to both sides there will be more supporting forces to make it stable.

双语君立扫把翻车现场

当地时间周二，面对世界各地吃瓜群众的空前热情，NASA亲自下场辟谣了。

In a video tweeted out by NASA's official account on Tuesday, astronaut Alvin Drew and scientist Sarah Noble balance a broom on its bristles with no fuss. 

周二NASA官方账号发布的视频推文中，宇航员Alvin Drew和科学家Sarah Noble丝毫不慌地立住了一把扫帚。

两位还贡献了一波吐槽：

'Did you do the broomstick challenge yesterday?' Noble asks. 'Well, it turns out, you can do it again today.'

Noble问，“你参加昨天的立扫把挑战了吗？结果是，你今天也能立住。”

And Drew responds, 'It's just physics.'

Drew表示，“不过是物理原理而已。”

记者：张周项

编辑：唐晓敏

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