独木船的加速度方向如何？
为了方便，正方向设为向下，方向如何取并不打紧，还有重力mg的-，作用。
And just for my convenience I call this now the plus direction just for my convenience — it doesn't really matter So now we have here mg — that is gravity acting upon you.
人们需要领导者来指引方向，有时对方向如何倒是不太在意，只要有人指引即可。
People need a leader, Sometimes it doesn't matter in which direction you point as long as someone is pointing.
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