object is in an unstable gravitational equilibrium, which means that if it stays perfectly put,

一個非常堅硬的環 繞著一個球對稱的物體

it’s fine, but if it gets nudged even just slightly off its perfectly centered position,

在重力的作用下是不穩定平衡的

it will then get pulled farther and farther from that position, since the part now closer

也就是說 如果它的位置完美的放在正中央

to the earth gets pulled more strongly toward the earth than the part now farther from earth.

那就OK

So, it’s just like a perfectly balanced pencil.

但如果它被輕輕推擠，稍微偏離了正中的位置