我们知道，地球是一个椭球体，但在一般计算中我们却常常把它近似地看成一个球体，其半径比一个篮球的半径要大得多．现在的问题是：假如可以沿赤道做一个大金属圈，沿篮球的大圆也做一个金属圈，再把两个圈都增加１米，则这两个金属圈与原物体之间就都有了空隙．再仅如金属圈 We know that the earth is an ellipsoid, but in general calculations we often think of it as a sphere with a radius much larger than the radius of a basketball. The question now is: If you can make a big metal ring along the equator, make a metal ring along the big circle of basketball, and increase both circles by 1 meter, then there will be a gap between the two metal rings and the original object. Voids. Just like a metal ring