那么究竟为什么扫帚能立住呢？

　　▌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：

　　▌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.