The fact that you don't need a force for it to move forever at a given speed in a given direction, that's not obvious, because in daily life you don't see that.

对于物体不需要力的作用就能保持,确定的速度和方向持续运动这一事实,它并非显而易见,因为在日常生活中你看不到这种情况

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because you need to know like, how fast the shutter speed and all that stuff,

因为你必须知道，像快门的速度，还有其他这一类东西，

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