事实上，我们推断蝙蝠在分析回声时过滤掉了很多因素，就像一个复杂的雷达系统可以忽略地面上静止物体的回声那样。

In fact, we kind of assumed that they were filtering a lot out, the way a sophisticated radar system can ignore echoes from stationary objects on the ground.

youdao

地面是一个静止的立方体，这是Box2D已知的，因为这个立方体的质量为零(默认)，因此不会与其他物体相撞。

The ground is a box that is static, which Box2D knows, because the box has zero mass (by default) and therefore doesn't collide with other objects.

youdao

“每一个物体保持其静止状态…除非有加于其上的力，它才会改变那种状态”(伊萨克·牛顿)。

"Every body continues in its state of rest... Unless it is compelled to change that state by forces impressed upon it" (Isaac Newton).

youdao

The Law of Inertia says that, "If a body has no forces acting on it, then it will remain at rest if it was at rest to begin with, or if it had a velocity to begin with, it will maintain that velocity."

惯性定律就是,"如果一个物体不受外力作用,那么静止的物体依然保持静止,如果物体有个初速度,那么就保持此速度不变"

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